using System;
using System.Diagnostics;
using System.Text;

using Bitmask = System.UInt64;

using i16 = System.Int16;
using u8 = System.Byte;
using u16 = System.UInt16;
using u32 = System.UInt32;

using sqlite3_int64 = System.Int64;

namespace Community.CsharpSqlite
{
  using sqlite3_value = Sqlite3.Mem;
  public partial class Sqlite3
  {
    /*
    ** 2001 September 15
    **
    ** The author disclaims copyright to this source code.  In place of
    ** a legal notice, here is a blessing:
    **
    **    May you do good and not evil.
    **    May you find forgiveness for yourself and forgive others.
    **    May you share freely, never taking more than you give.
    **
    *************************************************************************
    ** This module contains C code that generates VDBE code used to process
    ** the WHERE clause of SQL statements.  This module is responsible for
    ** generating the code that loops through a table looking for applicable
    ** rows.  Indices are selected and used to speed the search when doing
    ** so is applicable.  Because this module is responsible for selecting
    ** indices, you might also think of this module as the "query optimizer".
    *************************************************************************
    **  Included in SQLite3 port to C#-SQLite;  2008 Noah B Hart
    **  C#-SQLite is an independent reimplementation of the SQLite software library
    **
    **  SQLITE_SOURCE_ID: 2011-05-19 13:26:54 ed1da510a239ea767a01dc332b667119fa3c908ecd7
    **
    *************************************************************************
    */
    //#include "sqliteInt.h"


    /*
    ** Trace output macros
    */
#if  (SQLITE_TEST) || (SQLITE_DEBUG)
    static bool sqlite3WhereTrace = false;
#endif
#if  (SQLITE_TEST) && (SQLITE_DEBUG) && TRACE
//# define WHERETRACE(X)  if(sqlite3WhereTrace) sqlite3DebugPrintf X
static void WHERETRACE( string X, params object[] ap ) { if ( sqlite3WhereTrace ) sqlite3DebugPrintf( X, ap ); }
#else
    //# define WHERETRACE(X)
    static void WHERETRACE( string X, params object[] ap )
    {
    }
#endif

    /* Forward reference
*/
    //typedef struct WhereClause WhereClause;
    //typedef struct WhereMaskSet WhereMaskSet;
    //typedef struct WhereOrInfo WhereOrInfo;
    //typedef struct WhereAndInfo WhereAndInfo;
    //typedef struct WhereCost WhereCost;

    /*
    ** The query generator uses an array of instances of this structure to
    ** help it analyze the subexpressions of the WHERE clause.  Each WHERE
    ** clause subexpression is separated from the others by AND operators,
    ** usually, or sometimes subexpressions separated by OR.
    **
    ** All WhereTerms are collected into a single WhereClause structure.
    ** The following identity holds:
    **
    **        WhereTerm.pWC.a[WhereTerm.idx] == WhereTerm
    **
    ** When a term is of the form:
    **
    **              X <op> <expr>
    **
    ** where X is a column name and <op> is one of certain operators,
    ** then WhereTerm.leftCursor and WhereTerm.u.leftColumn record the
    ** cursor number and column number for X.  WhereTerm.eOperator records
    ** the <op> using a bitmask encoding defined by WO_xxx below.  The
    ** use of a bitmask encoding for the operator allows us to search
    ** quickly for terms that match any of several different operators.
    **
    ** A WhereTerm might also be two or more subterms connected by OR:
    **
    **         (t1.X <op> <expr>) OR (t1.Y <op> <expr>) OR ....
    **
    ** In this second case, wtFlag as the TERM_ORINFO set and eOperator==WO_OR
    ** and the WhereTerm.u.pOrInfo field points to auxiliary information that
    ** is collected about the
    **
    ** If a term in the WHERE clause does not match either of the two previous
    ** categories, then eOperator==0.  The WhereTerm.pExpr field is still set
    ** to the original subexpression content and wtFlags is set up appropriately
    ** but no other fields in the WhereTerm object are meaningful.
    **
    ** When eOperator!=0, prereqRight and prereqAll record sets of cursor numbers,
    ** but they do so indirectly.  A single WhereMaskSet structure translates
    ** cursor number into bits and the translated bit is stored in the prereq
    ** fields.  The translation is used in order to maximize the number of
    ** bits that will fit in a Bitmask.  The VDBE cursor numbers might be
    ** spread out over the non-negative integers.  For example, the cursor
    ** numbers might be 3, 8, 9, 10, 20, 23, 41, and 45.  The WhereMaskSet
    ** translates these sparse cursor numbers into consecutive integers
    ** beginning with 0 in order to make the best possible use of the available
    ** bits in the Bitmask.  So, in the example above, the cursor numbers
    ** would be mapped into integers 0 through 7.
    **
    ** The number of terms in a join is limited by the number of bits
    ** in prereqRight and prereqAll.  The default is 64 bits, hence SQLite
    ** is only able to process joins with 64 or fewer tables.
    */
    //typedef struct WhereTerm WhereTerm;
    public class WhereTerm
    {
      public Expr pExpr;              /* Pointer to the subexpression that is this term */
      public int iParent;             /* Disable pWC.a[iParent] when this term disabled */
      public int leftCursor;          /* Cursor number of X in "X <op> <expr>" */
      public class _u
      {
        public int leftColumn;        /* Column number of X in "X <op> <expr>" */
        public WhereOrInfo pOrInfo;   /* Extra information if eOperator==WO_OR */
        public WhereAndInfo pAndInfo; /* Extra information if eOperator==WO_AND */
      }
      public _u u = new _u();
      public u16 eOperator;          /* A WO_xx value describing <op> */
      public u8 wtFlags;             /* TERM_xxx bit flags.  See below */
      public u8 nChild;              /* Number of children that must disable us */
      public WhereClause pWC;        /* The clause this term is part of */
      public Bitmask prereqRight;    /* Bitmask of tables used by pExpr.pRight */
      public Bitmask prereqAll;      /* Bitmask of tables referenced by pExpr */
    };

    /*
    ** Allowed values of WhereTerm.wtFlags
    */
    //#define TERM_DYNAMIC    0x01   /* Need to call sqlite3ExprDelete(db, ref pExpr) */
    //#define TERM_VIRTUAL    0x02   /* Added by the optimizer.  Do not code */
    //#define TERM_CODED      0x04   /* This term is already coded */
    //#define TERM_COPIED     0x08   /* Has a child */
    //#define TERM_ORINFO     0x10   /* Need to free the WhereTerm.u.pOrInfo object */
    //#define TERM_ANDINFO    0x20   /* Need to free the WhereTerm.u.pAndInfo obj */
    //#define TERM_OR_OK      0x40   /* Used during OR-clause processing */
#if SQLITE_ENABLE_STAT2
    //#  define TERM_VNULL    0x80   /* Manufactured x>NULL or x<=NULL term */
#else
//#  define TERM_VNULL    0x00   /* Disabled if not using stat2 */
#endif
    const int TERM_DYNAMIC = 0x01; /* Need to call sqlite3ExprDelete(db, ref pExpr) */
    const int TERM_VIRTUAL = 0x02; /* Added by the optimizer.  Do not code */
    const int TERM_CODED = 0x04; /* This term is already coded */
    const int TERM_COPIED = 0x08; /* Has a child */
    const int TERM_ORINFO = 0x10; /* Need to free the WhereTerm.u.pOrInfo object */
    const int TERM_ANDINFO = 0x20; /* Need to free the WhereTerm.u.pAndInfo obj */
    const int TERM_OR_OK = 0x40; /* Used during OR-clause processing */
#if SQLITE_ENABLE_STAT2
    const int TERM_VNULL = 0x80;  /* Manufactured x>NULL or x<=NULL term */
#else
    const int TERM_VNULL = 0x00;  /* Disabled if not using stat2 */
#endif

    /*
    ** An instance of the following structure holds all information about a
    ** WHERE clause.  Mostly this is a container for one or more WhereTerms.
    */
    public class WhereClause
    {
      public Parse pParse;                              /* The parser context */
      public WhereMaskSet pMaskSet;                     /* Mapping of table cursor numbers to bitmasks */
      public Bitmask vmask;                             /* Bitmask identifying virtual table cursors */
      public u8 op;                                     /* Split operator.  TK_AND or TK_OR */
      public int nTerm;                                 /* Number of terms */
      public int nSlot;                                 /* Number of entries in a[] */
      public WhereTerm[] a;                             /* Each a[] describes a term of the WHERE cluase */
#if (SQLITE_SMALL_STACK)
public WhereTerm[] aStatic = new WhereTerm[1];    /* Initial static space for a[] */
#else
      public WhereTerm[] aStatic = new WhereTerm[8];    /* Initial static space for a[] */
#endif

      public void CopyTo( WhereClause wc )
      {
        wc.pParse = this.pParse;
        wc.pMaskSet = new WhereMaskSet();
        this.pMaskSet.CopyTo( wc.pMaskSet );
        wc.op = this.op;
        wc.nTerm = this.nTerm;
        wc.nSlot = this.nSlot;
        wc.a = (WhereTerm[])this.a.Clone();
        wc.aStatic = (WhereTerm[])this.aStatic.Clone();
      }
    };

    /*
    ** A WhereTerm with eOperator==WO_OR has its u.pOrInfo pointer set to
    ** a dynamically allocated instance of the following structure.
    */
    public class WhereOrInfo
    {
      public WhereClause wc = new WhereClause();/* Decomposition into subterms */
      public Bitmask indexable;                 /* Bitmask of all indexable tables in the clause */
    };

    /*
    ** A WhereTerm with eOperator==WO_AND has its u.pAndInfo pointer set to
    ** a dynamically allocated instance of the following structure.
    */
    public class WhereAndInfo
    {
      public WhereClause wc = new WhereClause();          /* The subexpression broken out */
    };

    /*
    ** An instance of the following structure keeps track of a mapping
    ** between VDBE cursor numbers and bits of the bitmasks in WhereTerm.
    **
    ** The VDBE cursor numbers are small integers contained in
    ** SrcList_item.iCursor and Expr.iTable fields.  For any given WHERE
    ** clause, the cursor numbers might not begin with 0 and they might
    ** contain gaps in the numbering sequence.  But we want to make maximum
    ** use of the bits in our bitmasks.  This structure provides a mapping
    ** from the sparse cursor numbers into consecutive integers beginning
    ** with 0.
    **
    ** If WhereMaskSet.ix[A]==B it means that The A-th bit of a Bitmask
    ** corresponds VDBE cursor number B.  The A-th bit of a bitmask is 1<<A.
    **
    ** For example, if the WHERE clause expression used these VDBE
    ** cursors:  4, 5, 8, 29, 57, 73.  Then the  WhereMaskSet structure
    ** would map those cursor numbers into bits 0 through 5.
    **
    ** Note that the mapping is not necessarily ordered.  In the example
    ** above, the mapping might go like this:  4.3, 5.1, 8.2, 29.0,
    ** 57.5, 73.4.  Or one of 719 other combinations might be used. It
    ** does not really matter.  What is important is that sparse cursor
    ** numbers all get mapped into bit numbers that begin with 0 and contain
    ** no gaps.
    */
    public class WhereMaskSet
    {
      public int n;                        /* Number of Debug.Assigned cursor values */
      public int[] ix = new int[BMS];       /* Cursor Debug.Assigned to each bit */

      public void CopyTo( WhereMaskSet wms )
      {
        wms.n = this.n;
        wms.ix = (int[])this.ix.Clone();
      }
    }

    /*
    ** A WhereCost object records a lookup strategy and the estimated
    ** cost of pursuing that strategy.
    */
    public class WhereCost
    {
      public WherePlan plan = new WherePlan();/* The lookup strategy */
      public double rCost;                    /* Overall cost of pursuing this search strategy */
      public Bitmask used;                    /* Bitmask of cursors used by this plan */

      public void Clear()
      {
        plan.Clear();
        rCost = 0;
        used = 0;
      }
    };

    /*
    ** Bitmasks for the operators that indices are able to exploit.  An
    ** OR-ed combination of these values can be used when searching for
    ** terms in the where clause.
    */
    //#define WO_IN     0x001
    //#define WO_EQ     0x002
    //#define WO_LT     (WO_EQ<<(TK_LT-TK_EQ))
    //#define WO_LE     (WO_EQ<<(TK_LE-TK_EQ))
    //#define WO_GT     (WO_EQ<<(TK_GT-TK_EQ))
    //#define WO_GE     (WO_EQ<<(TK_GE-TK_EQ))
    //#define WO_MATCH  0x040
    //#define WO_ISNULL 0x080
    //#define WO_OR     0x100       /* Two or more OR-connected terms */
    //#define WO_AND    0x200       /* Two or more AND-connected terms */
    //#define WO_NOOP   0x800       /* This term does not restrict search space */

    //#define WO_ALL    0xfff       /* Mask of all possible WO_* values */
    //#define WO_SINGLE 0x0ff       /* Mask of all non-compound WO_* values */
    const int WO_IN = 0x001;
    const int WO_EQ = 0x002;
    const int WO_LT = ( WO_EQ << ( TK_LT - TK_EQ ) );
    const int WO_LE = ( WO_EQ << ( TK_LE - TK_EQ ) );
    const int WO_GT = ( WO_EQ << ( TK_GT - TK_EQ ) );
    const int WO_GE = ( WO_EQ << ( TK_GE - TK_EQ ) );
    const int WO_MATCH = 0x040;
    const int WO_ISNULL = 0x080;
    const int WO_OR = 0x100;       /* Two or more OR-connected terms */
    const int WO_AND = 0x200;      /* Two or more AND-connected terms */
    const int WO_NOOP = 0x800;     /* This term does not restrict search space */

    const int WO_ALL = 0xfff;       /* Mask of all possible WO_* values */
    const int WO_SINGLE = 0x0ff;       /* Mask of all non-compound WO_* values */
    /*
    ** Value for wsFlags returned by bestIndex() and stored in
    ** WhereLevel.wsFlags.  These flags determine which search
    ** strategies are appropriate.
    **
    ** The least significant 12 bits is reserved as a mask for WO_ values above.
    ** The WhereLevel.wsFlags field is usually set to WO_IN|WO_EQ|WO_ISNULL.
    ** But if the table is the right table of a left join, WhereLevel.wsFlags
    ** is set to WO_IN|WO_EQ.  The WhereLevel.wsFlags field can then be used as
    ** the "op" parameter to findTerm when we are resolving equality constraints.
    ** ISNULL constraints will then not be used on the right table of a left
    ** join.  Tickets #2177 and #2189.
    */
    //#define WHERE_ROWID_EQ     0x00001000  /* rowid=EXPR or rowid IN (...) */
    //#define WHERE_ROWID_RANGE  0x00002000  /* rowid<EXPR and/or rowid>EXPR */
    //#define WHERE_COLUMN_EQ    0x00010000  /* x=EXPR or x IN (...) or x IS NULL */
    //#define WHERE_COLUMN_RANGE 0x00020000  /* x<EXPR and/or x>EXPR */
    //#define WHERE_COLUMN_IN    0x00040000  /* x IN (...) */
    //#define WHERE_COLUMN_NULL  0x00080000  /* x IS NULL */
    //#define WHERE_INDEXED      0x000f0000  /* Anything that uses an index */
    //#define WHERE_IN_ABLE      0x000f1000  /* Able to support an IN operator */
    //#define WHERE_NOT_FULLSCAN 0x100f3000  /* Does not do a full table scan */
    //#define WHERE_TOP_LIMIT    0x00100000  /* x<EXPR or x<=EXPR constraint */
    //#define WHERE_BTM_LIMIT    0x00200000  /* x>EXPR or x>=EXPR constraint */
    //#define WHERE_BOTH_LIMIT   0x00300000  /* Both x>EXPR and x<EXPR */
    //#define WHERE_IDX_ONLY     0x00800000  /* Use index only - omit table */
    //#define WHERE_ORDERBY      0x01000000  /* Output will appear in correct order */
    //#define WHERE_REVERSE      0x02000000  /* Scan in reverse order */
    //#define WHERE_UNIQUE       0x04000000  /* Selects no more than one row */
    //#define WHERE_VIRTUALTABLE 0x08000000  /* Use virtual-table processing */
    //#define WHERE_MULTI_OR     0x10000000  /* OR using multiple indices */
    //#define WHERE_TEMP_INDEX   0x20000000  /* Uses an ephemeral index */
    const int WHERE_ROWID_EQ = 0x00001000;
    const int WHERE_ROWID_RANGE = 0x00002000;
    const int WHERE_COLUMN_EQ = 0x00010000;
    const int WHERE_COLUMN_RANGE = 0x00020000;
    const int WHERE_COLUMN_IN = 0x00040000;
    const int WHERE_COLUMN_NULL = 0x00080000;
    const int WHERE_INDEXED = 0x000f0000;
    const int WHERE_IN_ABLE = 0x000f1000;
    const int WHERE_NOT_FULLSCAN = 0x100f3000;
    const int WHERE_TOP_LIMIT = 0x00100000;
    const int WHERE_BTM_LIMIT = 0x00200000;
    const int WHERE_BOTH_LIMIT = 0x00300000;
    const int WHERE_IDX_ONLY = 0x00800000;
    const int WHERE_ORDERBY = 0x01000000;
    const int WHERE_REVERSE = 0x02000000;
    const int WHERE_UNIQUE = 0x04000000;
    const int WHERE_VIRTUALTABLE = 0x08000000;
    const int WHERE_MULTI_OR = 0x10000000;
    const int WHERE_TEMP_INDEX = 0x20000000;

    /*
    ** Initialize a preallocated WhereClause structure.
    */
    static void whereClauseInit(
    WhereClause pWC,        /* The WhereClause to be initialized */
    Parse pParse,           /* The parsing context */
    WhereMaskSet pMaskSet   /* Mapping from table cursor numbers to bitmasks */
    )
    {
      pWC.pParse = pParse;
      pWC.pMaskSet = pMaskSet;
      pWC.nTerm = 0;
      pWC.nSlot = ArraySize( pWC.aStatic ) - 1;
      pWC.a = pWC.aStatic;
      pWC.vmask = 0;
    }

    /* Forward reference */
    //static void whereClauseClear(WhereClause);

    /*
    ** Deallocate all memory Debug.Associated with a WhereOrInfo object.
    */
    static void whereOrInfoDelete( sqlite3 db, WhereOrInfo p )
    {
      whereClauseClear( p.wc );
      sqlite3DbFree( db, ref p );
    }

    /*
    ** Deallocate all memory Debug.Associated with a WhereAndInfo object.
    */
    static void whereAndInfoDelete( sqlite3 db, WhereAndInfo p )
    {
      whereClauseClear( p.wc );
      sqlite3DbFree( db, ref p );
    }

    /*
    ** Deallocate a WhereClause structure.  The WhereClause structure
    ** itself is not freed.  This routine is the inverse of whereClauseInit().
    */
    static void whereClauseClear( WhereClause pWC )
    {
      int i;
      WhereTerm a;
      sqlite3 db = pWC.pParse.db;
      for ( i = pWC.nTerm - 1; i >= 0; i-- )//, a++)
      {
        a = pWC.a[i];
        if ( ( a.wtFlags & TERM_DYNAMIC ) != 0 )
        {
          sqlite3ExprDelete( db, ref a.pExpr );
        }
        if ( ( a.wtFlags & TERM_ORINFO ) != 0 )
        {
          whereOrInfoDelete( db, a.u.pOrInfo );
        }
        else if ( ( a.wtFlags & TERM_ANDINFO ) != 0 )
        {
          whereAndInfoDelete( db, a.u.pAndInfo );
        }
      }
      if ( pWC.a != pWC.aStatic )
      {
        sqlite3DbFree( db, ref pWC.a );
      }
    }

    /*
    ** Add a single new WhereTerm entry to the WhereClause object pWC.
    ** The new WhereTerm object is constructed from Expr p and with wtFlags.
    ** The index in pWC.a[] of the new WhereTerm is returned on success.
    ** 0 is returned if the new WhereTerm could not be added due to a memory
    ** allocation error.  The memory allocation failure will be recorded in
    ** the db.mallocFailed flag so that higher-level functions can detect it.
    **
    ** This routine will increase the size of the pWC.a[] array as necessary.
    **
    ** If the wtFlags argument includes TERM_DYNAMIC, then responsibility
    ** for freeing the expression p is Debug.Assumed by the WhereClause object pWC.
    ** This is true even if this routine fails to allocate a new WhereTerm.
    **
    ** WARNING:  This routine might reallocate the space used to store
    ** WhereTerms.  All pointers to WhereTerms should be invalidated after
    ** calling this routine.  Such pointers may be reinitialized by referencing
    ** the pWC.a[] array.
    */
    static int whereClauseInsert( WhereClause pWC, Expr p, u8 wtFlags )
    {
      WhereTerm pTerm;
      int idx;
      testcase( wtFlags & TERM_VIRTUAL );  /* EV: R-00211-15100 */
      if ( pWC.nTerm >= pWC.nSlot )
      {
        //WhereTerm pOld = pWC.a;
        //sqlite3 db = pWC.pParse.db;
        Array.Resize( ref pWC.a, pWC.nSlot * 2 );
        //pWC.a = sqlite3DbMallocRaw(db, sizeof(pWC.a[0])*pWC.nSlot*2 );
        //if( pWC.a==null ){
        //  if( wtFlags & TERM_DYNAMIC ){
        //    sqlite3ExprDelete(db, ref p);
        //  }
        //  pWC.a = pOld;
        //  return 0;
        //}
        //memcpy(pWC.a, pOld, sizeof(pWC.a[0])*pWC.nTerm);
        //if( pOld!=pWC.aStatic ){
        //  sqlite3DbFree(db, ref pOld);
        //}
        //pWC.nSlot = sqlite3DbMallocSize(db, pWC.a)/sizeof(pWC.a[0]);
        pWC.nSlot = pWC.a.Length - 1;
      }
      pWC.a[idx = pWC.nTerm++] = new WhereTerm();
      pTerm = pWC.a[idx];
      pTerm.pExpr = p;
      pTerm.wtFlags = wtFlags;
      pTerm.pWC = pWC;
      pTerm.iParent = -1;
      return idx;
    }

    /*
    ** This routine identifies subexpressions in the WHERE clause where
    ** each subexpression is separated by the AND operator or some other
    ** operator specified in the op parameter.  The WhereClause structure
    ** is filled with pointers to subexpressions.  For example:
    **
    **    WHERE  a=='hello' AND coalesce(b,11)<10 AND (c+12!=d OR c==22)
    **           \________/     \_______________/     \________________/
    **            slot[0]            slot[1]               slot[2]
    **
    ** The original WHERE clause in pExpr is unaltered.  All this routine
    ** does is make slot[] entries point to substructure within pExpr.
    **
    ** In the previous sentence and in the diagram, "slot[]" refers to
    ** the WhereClause.a[] array.  The slot[] array grows as needed to contain
    ** all terms of the WHERE clause.
    */
    static void whereSplit( WhereClause pWC, Expr pExpr, int op )
    {
      pWC.op = (u8)op;
      if ( pExpr == null )
        return;
      if ( pExpr.op != op )
      {
        whereClauseInsert( pWC, pExpr, 0 );
      }
      else
      {
        whereSplit( pWC, pExpr.pLeft, op );
        whereSplit( pWC, pExpr.pRight, op );
      }
    }

    /*
    ** Initialize an expression mask set (a WhereMaskSet object)
    */
    //#define initMaskSet(P)  memset(P, 0, sizeof(*P))

    /*
    ** Return the bitmask for the given cursor number.  Return 0 if
    ** iCursor is not in the set.
    */
    static Bitmask getMask( WhereMaskSet pMaskSet, int iCursor )
    {
      int i;
      Debug.Assert( pMaskSet.n <= (int)sizeof( Bitmask ) * 8 );
      for ( i = 0; i < pMaskSet.n; i++ )
      {
        if ( pMaskSet.ix[i] == iCursor )
        {
          return ( (Bitmask)1 ) << i;
        }
      }
      return 0;
    }

    /*
    ** Create a new mask for cursor iCursor.
    **
    ** There is one cursor per table in the FROM clause.  The number of
    ** tables in the FROM clause is limited by a test early in the
    ** sqlite3WhereBegin() routine.  So we know that the pMaskSet.ix[]
    ** array will never overflow.
    */
    static void createMask( WhereMaskSet pMaskSet, int iCursor )
    {
      Debug.Assert( pMaskSet.n < ArraySize( pMaskSet.ix ) );
      pMaskSet.ix[pMaskSet.n++] = iCursor;
    }

    /*
    ** This routine walks (recursively) an expression tree and generates
    ** a bitmask indicating which tables are used in that expression
    ** tree.
    **
    ** In order for this routine to work, the calling function must have
    ** previously invoked sqlite3ResolveExprNames() on the expression.  See
    ** the header comment on that routine for additional information.
    ** The sqlite3ResolveExprNames() routines looks for column names and
    ** sets their opcodes to TK_COLUMN and their Expr.iTable fields to
    ** the VDBE cursor number of the table.  This routine just has to
    ** translate the cursor numbers into bitmask values and OR all
    ** the bitmasks together.
    */
    //static Bitmask exprListTableUsage(WhereMaskSet*, ExprList);
    //static Bitmask exprSelectTableUsage(WhereMaskSet*, Select);
    static Bitmask exprTableUsage( WhereMaskSet pMaskSet, Expr p )
    {
      Bitmask mask = 0;
      if ( p == null )
        return 0;
      if ( p.op == TK_COLUMN )
      {
        mask = getMask( pMaskSet, p.iTable );
        return mask;
      }
      mask = exprTableUsage( pMaskSet, p.pRight );
      mask |= exprTableUsage( pMaskSet, p.pLeft );
      if ( ExprHasProperty( p, EP_xIsSelect ) )
      {
        mask |= exprSelectTableUsage( pMaskSet, p.x.pSelect );
      }
      else
      {
        mask |= exprListTableUsage( pMaskSet, p.x.pList );
      }
      return mask;
    }
    static Bitmask exprListTableUsage( WhereMaskSet pMaskSet, ExprList pList )
    {
      int i;
      Bitmask mask = 0;
      if ( pList != null )
      {
        for ( i = 0; i < pList.nExpr; i++ )
        {
          mask |= exprTableUsage( pMaskSet, pList.a[i].pExpr );
        }
      }
      return mask;
    }
    static Bitmask exprSelectTableUsage( WhereMaskSet pMaskSet, Select pS )
    {
      Bitmask mask = 0;
      while ( pS != null )
      {
        mask |= exprListTableUsage( pMaskSet, pS.pEList );
        mask |= exprListTableUsage( pMaskSet, pS.pGroupBy );
        mask |= exprListTableUsage( pMaskSet, pS.pOrderBy );
        mask |= exprTableUsage( pMaskSet, pS.pWhere );
        mask |= exprTableUsage( pMaskSet, pS.pHaving );
        pS = pS.pPrior;
      }
      return mask;
    }

    /*
    ** Return TRUE if the given operator is one of the operators that is
    ** allowed for an indexable WHERE clause term.  The allowed operators are
    ** "=", "<", ">", "<=", ">=", and "IN".
    **
    ** IMPLEMENTATION-OF: R-59926-26393 To be usable by an index a term must be
    ** of one of the following forms: column = expression column > expression
    ** column >= expression column < expression column <= expression
    ** expression = column expression > column expression >= column
    ** expression < column expression <= column column IN
    ** (expression-list) column IN (subquery) column IS NULL
    */
    static bool allowedOp( int op )
    {
      Debug.Assert( TK_GT > TK_EQ && TK_GT < TK_GE );
      Debug.Assert( TK_LT > TK_EQ && TK_LT < TK_GE );
      Debug.Assert( TK_LE > TK_EQ && TK_LE < TK_GE );
      Debug.Assert( TK_GE == TK_EQ + 4 );
      return op == TK_IN || ( op >= TK_EQ && op <= TK_GE ) || op == TK_ISNULL;
    }

    /*
    ** Swap two objects of type TYPE.
    */
    //#define SWAP(TYPE,A,B) {TYPE t=A; A=B; B=t;}

    /*
    ** Commute a comparison operator.  Expressions of the form "X op Y"
    ** are converted into "Y op X".
    **
    ** If a collation sequence is Debug.Associated with either the left or right
    ** side of the comparison, it remains Debug.Associated with the same side after
    ** the commutation. So "Y collate NOCASE op X" becomes
    ** "X collate NOCASE op Y". This is because any collation sequence on
    ** the left hand side of a comparison overrides any collation sequence
    ** attached to the right. For the same reason the EP_ExpCollate flag
    ** is not commuted.
    */
    static void exprCommute( Parse pParse, Expr pExpr )
    {
      u16 expRight = (u16)( pExpr.pRight.flags & EP_ExpCollate );
      u16 expLeft = (u16)( pExpr.pLeft.flags & EP_ExpCollate );
      Debug.Assert( allowedOp( pExpr.op ) && pExpr.op != TK_IN );
      pExpr.pRight.pColl = sqlite3ExprCollSeq( pParse, pExpr.pRight );
      pExpr.pLeft.pColl = sqlite3ExprCollSeq( pParse, pExpr.pLeft );
      SWAP( ref pExpr.pRight.pColl, ref pExpr.pLeft.pColl );
      pExpr.pRight.flags = (u16)( ( pExpr.pRight.flags & ~EP_ExpCollate ) | expLeft );
      pExpr.pLeft.flags = (u16)( ( pExpr.pLeft.flags & ~EP_ExpCollate ) | expRight );
      SWAP( ref pExpr.pRight, ref pExpr.pLeft );
      if ( pExpr.op >= TK_GT )
      {
        Debug.Assert( TK_LT == TK_GT + 2 );
        Debug.Assert( TK_GE == TK_LE + 2 );
        Debug.Assert( TK_GT > TK_EQ );
        Debug.Assert( TK_GT < TK_LE );
        Debug.Assert( pExpr.op >= TK_GT && pExpr.op <= TK_GE );
        pExpr.op = (u8)( ( ( pExpr.op - TK_GT ) ^ 2 ) + TK_GT );
      }
    }

    /*
    ** Translate from TK_xx operator to WO_xx bitmask.
    */
    static u16 operatorMask( int op )
    {
      u16 c;
      Debug.Assert( allowedOp( op ) );
      if ( op == TK_IN )
      {
        c = WO_IN;
      }
      else if ( op == TK_ISNULL )
      {
        c = WO_ISNULL;
      }
      else
      {
        Debug.Assert( ( WO_EQ << ( op - TK_EQ ) ) < 0x7fff );
        c = (u16)( WO_EQ << ( op - TK_EQ ) );
      }
      Debug.Assert( op != TK_ISNULL || c == WO_ISNULL );
      Debug.Assert( op != TK_IN || c == WO_IN );
      Debug.Assert( op != TK_EQ || c == WO_EQ );
      Debug.Assert( op != TK_LT || c == WO_LT );
      Debug.Assert( op != TK_LE || c == WO_LE );
      Debug.Assert( op != TK_GT || c == WO_GT );
      Debug.Assert( op != TK_GE || c == WO_GE );
      return c;
    }

    /*
    ** Search for a term in the WHERE clause that is of the form "X <op> <expr>"
    ** where X is a reference to the iColumn of table iCur and <op> is one of
    ** the WO_xx operator codes specified by the op parameter.
    ** Return a pointer to the term.  Return 0 if not found.
    */
    static WhereTerm findTerm(
    WhereClause pWC,     /* The WHERE clause to be searched */
    int iCur,             /* Cursor number of LHS */
    int iColumn,          /* Column number of LHS */
    Bitmask notReady,     /* RHS must not overlap with this mask */
    u32 op,               /* Mask of WO_xx values describing operator */
    Index pIdx           /* Must be compatible with this index, if not NULL */
    )
    {
      WhereTerm pTerm;
      int k;
      Debug.Assert( iCur >= 0 );
      op &= WO_ALL;
      for ( k = pWC.nTerm; k != 0; k-- )//, pTerm++)
      {
        pTerm = pWC.a[pWC.nTerm - k];
        if ( pTerm.leftCursor == iCur
        && ( pTerm.prereqRight & notReady ) == 0
        && pTerm.u.leftColumn == iColumn
        && ( pTerm.eOperator & op ) != 0
        )
        {
          if ( pIdx != null && pTerm.eOperator != WO_ISNULL )
          {
            Expr pX = pTerm.pExpr;
            CollSeq pColl;
            char idxaff;
            int j;
            Parse pParse = pWC.pParse;

            idxaff = pIdx.pTable.aCol[iColumn].affinity;
            if ( !sqlite3IndexAffinityOk( pX, idxaff ) )
              continue;

            /* Figure out the collation sequence required from an index for
            ** it to be useful for optimising expression pX. Store this
            ** value in variable pColl.
            */
            Debug.Assert( pX.pLeft != null );
            pColl = sqlite3BinaryCompareCollSeq( pParse, pX.pLeft, pX.pRight );
            Debug.Assert( pColl != null || pParse.nErr != 0 );

            for ( j = 0; pIdx.aiColumn[j] != iColumn; j++ )
            {
              if ( NEVER( j >= pIdx.nColumn ) )
                return null;
            }
            if ( pColl != null && !pColl.zName.Equals( pIdx.azColl[j], StringComparison.OrdinalIgnoreCase ) )
              continue;
          }
          return pTerm;
        }
      }
      return null;
    }

    /* Forward reference */
    //static void exprAnalyze(SrcList*, WhereClause*, int);

    /*
    ** Call exprAnalyze on all terms in a WHERE clause.
    **
    **
    */
    static void exprAnalyzeAll(
    SrcList pTabList,       /* the FROM clause */
    WhereClause pWC         /* the WHERE clause to be analyzed */
    )
    {
      int i;
      for ( i = pWC.nTerm - 1; i >= 0; i-- )
      {
        exprAnalyze( pTabList, pWC, i );
      }
    }

#if  !SQLITE_OMIT_LIKE_OPTIMIZATION
    /*
** Check to see if the given expression is a LIKE or GLOB operator that
** can be optimized using inequality constraints.  Return TRUE if it is
** so and false if not.
**
** In order for the operator to be optimizible, the RHS must be a string
** literal that does not begin with a wildcard.
*/
    static int isLikeOrGlob(
    Parse pParse,         /* Parsing and code generating context */
    Expr pExpr,           /* Test this expression */
    ref Expr ppPrefix,    /* Pointer to TK_STRING expression with pattern prefix */
    ref bool pisComplete, /* True if the only wildcard is % in the last character */
    ref bool pnoCase      /* True if uppercase is equivalent to lowercase */
    )
    {
      string z = null;            /* String on RHS of LIKE operator */
      Expr pRight, pLeft;        /* Right and left size of LIKE operator */
      ExprList pList;            /* List of operands to the LIKE operator */
      int c = 0;                 /* One character in z[] */
      int cnt;                   /* Number of non-wildcard prefix characters */
      char[] wc = new char[3];   /* Wildcard characters */
      sqlite3 db = pParse.db;    /* Data_base connection */
      sqlite3_value pVal = null;
      int op;                    /* Opcode of pRight */

      if ( !sqlite3IsLikeFunction( db, pExpr, ref pnoCase, wc ) )
      {
        return 0;
      }
      //#if SQLITE_EBCDIC
      //if( pnoCase ) return 0;
      //#endif
      pList = pExpr.x.pList;
      pLeft = pList.a[1].pExpr;
      if ( pLeft.op != TK_COLUMN || sqlite3ExprAffinity( pLeft ) != SQLITE_AFF_TEXT )
      {
        /* IMP: R-02065-49465 The left-hand side of the LIKE or GLOB operator must
        ** be the name of an indexed column with TEXT affinity. */
        return 0;
      }
      Debug.Assert( pLeft.iColumn != ( -1 ) ); /* Because IPK never has AFF_TEXT */

      pRight = pList.a[0].pExpr;
      op = pRight.op;
      if ( op == TK_REGISTER )
      {
        op = pRight.op2;
      }
      if ( op == TK_VARIABLE )
      {
        Vdbe pReprepare = pParse.pReprepare;
        int iCol = pRight.iColumn;
        pVal = sqlite3VdbeGetValue( pReprepare, iCol, (byte)SQLITE_AFF_NONE );
        if ( pVal != null && sqlite3_value_type( pVal ) == SQLITE_TEXT )
        {
          z = sqlite3_value_text( pVal );
        }
        sqlite3VdbeSetVarmask( pParse.pVdbe, iCol ); /* IMP: R-23257-02778 */
        Debug.Assert( pRight.op == TK_VARIABLE || pRight.op == TK_REGISTER );
      }
      else if ( op == TK_STRING )
      {
        z = pRight.u.zToken;
      }
      if ( !string.IsNullOrEmpty( z ) )
      {
        cnt = 0;
        while ( cnt < z.Length && ( c = z[cnt] ) != 0 && c != wc[0] && c != wc[1] && c != wc[2] )
        {
          cnt++;
        }
        if ( cnt != 0 && 255 != (u8)z[cnt - 1] )
        {
          Expr pPrefix;
          pisComplete = c == wc[0] && cnt == z.Length - 1;
          pPrefix = sqlite3Expr( db, TK_STRING, z );
          if ( pPrefix != null )
            pPrefix.u.zToken = pPrefix.u.zToken.Substring( 0, cnt );
          ppPrefix = pPrefix;
          if ( op == TK_VARIABLE )
          {
            Vdbe v = pParse.pVdbe;
            sqlite3VdbeSetVarmask( v, pRight.iColumn ); /* IMP: R-23257-02778 */
            if ( pisComplete && pRight.u.zToken.Length > 1 )
            {
              /* If the rhs of the LIKE expression is a variable, and the current
              ** value of the variable means there is no need to invoke the LIKE
              ** function, then no OP_Variable will be added to the program.
              ** This causes problems for the sqlite3_bind_parameter_name()
              ** API. To workaround them, add a dummy OP_Variable here.
              */
              int r1 = sqlite3GetTempReg( pParse );
              sqlite3ExprCodeTarget( pParse, pRight, r1 );
              sqlite3VdbeChangeP3( v, sqlite3VdbeCurrentAddr( v ) - 1, 0 );
              sqlite3ReleaseTempReg( pParse, r1 );
            }
          }
        }
        else
        {
          z = null;
        }
      }

      sqlite3ValueFree( ref pVal );
      return ( z != null ) ? 1 : 0;
    }
#endif //* SQLITE_OMIT_LIKE_OPTIMIZATION */


#if  !SQLITE_OMIT_VIRTUALTABLE
/*
** Check to see if the given expression is of the form
**
**         column MATCH expr
**
** If it is then return TRUE.  If not, return FALSE.
*/
static int isMatchOfColumn(
Expr pExpr      /* Test this expression */
){
ExprList pList;

if( pExpr.op!=TK_FUNCTION ){
return 0;
}
if( !pExpr.u.zToken.Equals("match", StringComparison.OrdinalIgnoreCase ) ){
return 0;
}
pList = pExpr.x.pList;
if( pList.nExpr!=2 ){
  return 0;
}
if( pList.a[1].pExpr.op != TK_COLUMN ){
return 0;
}
return 1;
}
#endif //* SQLITE_OMIT_VIRTUALTABLE */

    /*
** If the pBase expression originated in the ON or USING clause of
** a join, then transfer the appropriate markings over to derived.
*/
    static void transferJoinMarkings( Expr pDerived, Expr pBase )
    {
      pDerived.flags = (u16)( pDerived.flags | pBase.flags & EP_FromJoin );
      pDerived.iRightJoinTable = pBase.iRightJoinTable;
    }

#if  !(SQLITE_OMIT_OR_OPTIMIZATION) && !(SQLITE_OMIT_SUBQUERY)
    /*
** Analyze a term that consists of two or more OR-connected
** subterms.  So in:
**
**     ... WHERE  (a=5) AND (b=7 OR c=9 OR d=13) AND (d=13)
**                          ^^^^^^^^^^^^^^^^^^^^
**
** This routine analyzes terms such as the middle term in the above example.
** A WhereOrTerm object is computed and attached to the term under
** analysis, regardless of the outcome of the analysis.  Hence:
**
**     WhereTerm.wtFlags   |=  TERM_ORINFO
**     WhereTerm.u.pOrInfo  =  a dynamically allocated WhereOrTerm object
**
** The term being analyzed must have two or more of OR-connected subterms.
** A single subterm might be a set of AND-connected sub-subterms.
** Examples of terms under analysis:
**
**     (A)     t1.x=t2.y OR t1.x=t2.z OR t1.y=15 OR t1.z=t3.a+5
**     (B)     x=expr1 OR expr2=x OR x=expr3
**     (C)     t1.x=t2.y OR (t1.x=t2.z AND t1.y=15)
**     (D)     x=expr1 OR (y>11 AND y<22 AND z LIKE '*hello*')
**     (E)     (p.a=1 AND q.b=2 AND r.c=3) OR (p.x=4 AND q.y=5 AND r.z=6)
**
** CASE 1:
**
** If all subterms are of the form T.C=expr for some single column of C
** a single table T (as shown in example B above) then create a new virtual
** term that is an equivalent IN expression.  In other words, if the term
** being analyzed is:
**
**      x = expr1  OR  expr2 = x  OR  x = expr3
**
** then create a new virtual term like this:
**
**      x IN (expr1,expr2,expr3)
**
** CASE 2:
**
** If all subterms are indexable by a single table T, then set
**
**     WhereTerm.eOperator              =  WO_OR
**     WhereTerm.u.pOrInfo.indexable  |=  the cursor number for table T
**
** A subterm is "indexable" if it is of the form
** "T.C <op> <expr>" where C is any column of table T and
** <op> is one of "=", "<", "<=", ">", ">=", "IS NULL", or "IN".
** A subterm is also indexable if it is an AND of two or more
** subsubterms at least one of which is indexable.  Indexable AND
** subterms have their eOperator set to WO_AND and they have
** u.pAndInfo set to a dynamically allocated WhereAndTerm object.
**
** From another point of view, "indexable" means that the subterm could
** potentially be used with an index if an appropriate index exists.
** This analysis does not consider whether or not the index exists; that
** is something the bestIndex() routine will determine.  This analysis
** only looks at whether subterms appropriate for indexing exist.
**
** All examples A through E above all satisfy case 2.  But if a term
** also statisfies case 1 (such as B) we know that the optimizer will
** always prefer case 1, so in that case we pretend that case 2 is not
** satisfied.
**
** It might be the case that multiple tables are indexable.  For example,
** (E) above is indexable on tables P, Q, and R.
**
** Terms that satisfy case 2 are candidates for lookup by using
** separate indices to find rowids for each subterm and composing
** the union of all rowids using a RowSet object.  This is similar
** to "bitmap indices" in other data_base engines.
**
** OTHERWISE:
**
** If neither case 1 nor case 2 apply, then leave the eOperator set to
** zero.  This term is not useful for search.
*/
    static void exprAnalyzeOrTerm(
    SrcList pSrc,            /* the FROM clause */
    WhereClause pWC,         /* the complete WHERE clause */
    int idxTerm               /* Index of the OR-term to be analyzed */
    )
    {
      Parse pParse = pWC.pParse;            /* Parser context */
      sqlite3 db = pParse.db;               /* Data_base connection */
      WhereTerm pTerm = pWC.a[idxTerm];    /* The term to be analyzed */
      Expr pExpr = pTerm.pExpr;             /* The expression of the term */
      WhereMaskSet pMaskSet = pWC.pMaskSet; /* Table use masks */
      int i;                                  /* Loop counters */
      WhereClause pOrWc;        /* Breakup of pTerm into subterms */
      WhereTerm pOrTerm;        /* A Sub-term within the pOrWc */
      WhereOrInfo pOrInfo;      /* Additional information Debug.Associated with pTerm */
      Bitmask chngToIN;         /* Tables that might satisfy case 1 */
      Bitmask indexable;        /* Tables that are indexable, satisfying case 2 */

      /*
      ** Break the OR clause into its separate subterms.  The subterms are
      ** stored in a WhereClause structure containing within the WhereOrInfo
      ** object that is attached to the original OR clause term.
      */
      Debug.Assert( ( pTerm.wtFlags & ( TERM_DYNAMIC | TERM_ORINFO | TERM_ANDINFO ) ) == 0 );
      Debug.Assert( pExpr.op == TK_OR );
      pTerm.u.pOrInfo = pOrInfo = new WhereOrInfo();//sqlite3DbMallocZero(db, sizeof(*pOrInfo));
      if ( pOrInfo == null )
        return;
      pTerm.wtFlags |= TERM_ORINFO;
      pOrWc = pOrInfo.wc;
      whereClauseInit( pOrWc, pWC.pParse, pMaskSet );
      whereSplit( pOrWc, pExpr, TK_OR );
      exprAnalyzeAll( pSrc, pOrWc );
      //      if ( db.mallocFailed != 0 ) return;
      Debug.Assert( pOrWc.nTerm >= 2 );

      /*
      ** Compute the set of tables that might satisfy cases 1 or 2.
      */
      indexable = ~(Bitmask)0;
      chngToIN = ~( pWC.vmask );
      for ( i = pOrWc.nTerm - 1; i >= 0 && indexable != 0; i-- )//, pOrTerm++ )
      {
        pOrTerm = pOrWc.a[i];
        if ( ( pOrTerm.eOperator & WO_SINGLE ) == 0 )
        {
          WhereAndInfo pAndInfo;
          Debug.Assert( pOrTerm.eOperator == 0 );
          Debug.Assert( ( pOrTerm.wtFlags & ( TERM_ANDINFO | TERM_ORINFO ) ) == 0 );
          chngToIN = 0;
          pAndInfo = new WhereAndInfo();//sqlite3DbMallocRaw(db, sizeof(*pAndInfo));
          if ( pAndInfo != null )
          {
            WhereClause pAndWC;
            WhereTerm pAndTerm;
            int j;
            Bitmask b = 0;
            pOrTerm.u.pAndInfo = pAndInfo;
            pOrTerm.wtFlags |= TERM_ANDINFO;
            pOrTerm.eOperator = WO_AND;
            pAndWC = pAndInfo.wc;
            whereClauseInit( pAndWC, pWC.pParse, pMaskSet );
            whereSplit( pAndWC, pOrTerm.pExpr, TK_AND );
            exprAnalyzeAll( pSrc, pAndWC );
            //testcase( db.mallocFailed );
            ////if ( 0 == db.mallocFailed )
            {
              for ( j = 0; j < pAndWC.nTerm; j++ )//, pAndTerm++ )
              {
                pAndTerm = pAndWC.a[j];
                Debug.Assert( pAndTerm.pExpr != null );
                if ( allowedOp( pAndTerm.pExpr.op ) )
                {
                  b |= getMask( pMaskSet, pAndTerm.leftCursor );
                }
              }
            }
            indexable &= b;
          }
        }
        else if ( ( pOrTerm.wtFlags & TERM_COPIED ) != 0 )
        {
          /* Skip this term for now.  We revisit it when we process the
          ** corresponding TERM_VIRTUAL term */
        }
        else
        {
          Bitmask b;
          b = getMask( pMaskSet, pOrTerm.leftCursor );
          if ( ( pOrTerm.wtFlags & TERM_VIRTUAL ) != 0 )
          {
            WhereTerm pOther = pOrWc.a[pOrTerm.iParent];
            b |= getMask( pMaskSet, pOther.leftCursor );
          }
          indexable &= b;
          if ( pOrTerm.eOperator != WO_EQ )
          {
            chngToIN = 0;
          }
          else
          {
            chngToIN &= b;
          }
        }
      }

      /*
      ** Record the set of tables that satisfy case 2.  The set might be
      ** empty.
      */
      pOrInfo.indexable = indexable;
      pTerm.eOperator = (u16)( indexable == 0 ? 0 : WO_OR );

      /*
      ** chngToIN holds a set of tables that *might* satisfy case 1.  But
      ** we have to do some additional checking to see if case 1 really
      ** is satisfied.
      **
      ** chngToIN will hold either 0, 1, or 2 bits.  The 0-bit case means
      ** that there is no possibility of transforming the OR clause into an
      ** IN operator because one or more terms in the OR clause contain
      ** something other than == on a column in the single table.  The 1-bit
      ** case means that every term of the OR clause is of the form
      ** "table.column=expr" for some single table.  The one bit that is set
      ** will correspond to the common table.  We still need to check to make
      ** sure the same column is used on all terms.  The 2-bit case is when
      ** the all terms are of the form "table1.column=table2.column".  It
      ** might be possible to form an IN operator with either table1.column
      ** or table2.column as the LHS if either is common to every term of
      ** the OR clause.
      **
      ** Note that terms of the form "table.column1=table.column2" (the
      ** same table on both sizes of the ==) cannot be optimized.
      */
      if ( chngToIN != 0 )
      {
        int okToChngToIN = 0;     /* True if the conversion to IN is valid */
        int iColumn = -1;         /* Column index on lhs of IN operator */
        int iCursor = -1;         /* Table cursor common to all terms */
        int j = 0;                /* Loop counter */

        /* Search for a table and column that appears on one side or the
        ** other of the == operator in every subterm.  That table and column
        ** will be recorded in iCursor and iColumn.  There might not be any
        ** such table and column.  Set okToChngToIN if an appropriate table
        ** and column is found but leave okToChngToIN false if not found.
        */
        for ( j = 0; j < 2 && 0 == okToChngToIN; j++ )
        {
          //pOrTerm = pOrWc.a;
          for ( i = pOrWc.nTerm - 1; i >= 0; i-- )//, pOrTerm++)
          {
            pOrTerm = pOrWc.a[pOrWc.nTerm - 1 - i];
            Debug.Assert( pOrTerm.eOperator == WO_EQ );
            pOrTerm.wtFlags = (u8)( pOrTerm.wtFlags & ~TERM_OR_OK );
            if ( pOrTerm.leftCursor == iCursor )
            {
              /* This is the 2-bit case and we are on the second iteration and
              ** current term is from the first iteration.  So skip this term. */
              Debug.Assert( j == 1 );
              continue;
            }
            if ( ( chngToIN & getMask( pMaskSet, pOrTerm.leftCursor ) ) == 0 )
            {
              /* This term must be of the form t1.a==t2.b where t2 is in the
              ** chngToIN set but t1 is not.  This term will be either preceeded
              ** or follwed by an inverted copy (t2.b==t1.a).  Skip this term
              ** and use its inversion. */
              testcase( pOrTerm.wtFlags & TERM_COPIED );
              testcase( pOrTerm.wtFlags & TERM_VIRTUAL );
              Debug.Assert( ( pOrTerm.wtFlags & ( TERM_COPIED | TERM_VIRTUAL ) ) != 0 );
              continue;
            }
            iColumn = pOrTerm.u.leftColumn;
            iCursor = pOrTerm.leftCursor;
            break;
          }
          if ( i < 0 )
          {
            /* No candidate table+column was found.  This can only occur
            ** on the second iteration */
            Debug.Assert( j == 1 );
            Debug.Assert( ( chngToIN & ( chngToIN - 1 ) ) == 0 );
            Debug.Assert( chngToIN == getMask( pMaskSet, iCursor ) );
            break;
          }
          testcase( j == 1 );

          /* We have found a candidate table and column.  Check to see if that
          ** table and column is common to every term in the OR clause */
          okToChngToIN = 1;
          for ( ; i >= 0 && okToChngToIN != 0; i-- )//, pOrTerm++)
          {
            pOrTerm = pOrWc.a[pOrWc.nTerm - 1 - i];
            Debug.Assert( pOrTerm.eOperator == WO_EQ );
            if ( pOrTerm.leftCursor != iCursor )
            {
              pOrTerm.wtFlags = (u8)( pOrTerm.wtFlags & ~TERM_OR_OK );
            }
            else if ( pOrTerm.u.leftColumn != iColumn )
            {
              okToChngToIN = 0;
            }
            else
            {
              int affLeft, affRight;
              /* If the right-hand side is also a column, then the affinities
              ** of both right and left sides must be such that no type
              ** conversions are required on the right.  (Ticket #2249)
              */
              affRight = sqlite3ExprAffinity( pOrTerm.pExpr.pRight );
              affLeft = sqlite3ExprAffinity( pOrTerm.pExpr.pLeft );
              if ( affRight != 0 && affRight != affLeft )
              {
                okToChngToIN = 0;
              }
              else
              {
                pOrTerm.wtFlags |= TERM_OR_OK;
              }
            }
          }
        }

        /* At this point, okToChngToIN is true if original pTerm satisfies
        ** case 1.  In that case, construct a new virtual term that is
        ** pTerm converted into an IN operator.
        **
        ** EV: R-00211-15100
        */
        if ( okToChngToIN != 0 )
        {
          Expr pDup;            /* A transient duplicate expression */
          ExprList pList = null;   /* The RHS of the IN operator */
          Expr pLeft = null;       /* The LHS of the IN operator */
          Expr pNew;            /* The complete IN operator */

          for ( i = pOrWc.nTerm - 1; i >= 0; i-- )//, pOrTerm++)
          {
            pOrTerm = pOrWc.a[pOrWc.nTerm - 1 - i];
            if ( ( pOrTerm.wtFlags & TERM_OR_OK ) == 0 )
              continue;
            Debug.Assert( pOrTerm.eOperator == WO_EQ );
            Debug.Assert( pOrTerm.leftCursor == iCursor );
            Debug.Assert( pOrTerm.u.leftColumn == iColumn );
            pDup = sqlite3ExprDup( db, pOrTerm.pExpr.pRight, 0 );
            pList = sqlite3ExprListAppend( pWC.pParse, pList, pDup );
            pLeft = pOrTerm.pExpr.pLeft;
          }
          Debug.Assert( pLeft != null );
          pDup = sqlite3ExprDup( db, pLeft, 0 );
          pNew = sqlite3PExpr( pParse, TK_IN, pDup, null, null );
          if ( pNew != null )
          {
            int idxNew;
            transferJoinMarkings( pNew, pExpr );
            Debug.Assert( !ExprHasProperty( pNew, EP_xIsSelect ) );
            pNew.x.pList = pList;
            idxNew = whereClauseInsert( pWC, pNew, TERM_VIRTUAL | TERM_DYNAMIC );
            testcase( idxNew == 0 );
            exprAnalyze( pSrc, pWC, idxNew );
            pTerm = pWC.a[idxTerm];
            pWC.a[idxNew].iParent = idxTerm;
            pTerm.nChild = 1;
          }
          else
          {
            sqlite3ExprListDelete( db, ref pList );
          }
          pTerm.eOperator = WO_NOOP;  /* case 1 trumps case 2 */
        }
      }
    }
#endif //* !SQLITE_OMIT_OR_OPTIMIZATION && !SQLITE_OMIT_SUBQUERY */


    /*
** The input to this routine is an WhereTerm structure with only the
** "pExpr" field filled in.  The job of this routine is to analyze the
** subexpression and populate all the other fields of the WhereTerm
** structure.
**
** If the expression is of the form "<expr> <op> X" it gets commuted
** to the standard form of "X <op> <expr>".
**
** If the expression is of the form "X <op> Y" where both X and Y are
** columns, then the original expression is unchanged and a new virtual
** term of the form "Y <op> X" is added to the WHERE clause and
** analyzed separately.  The original term is marked with TERM_COPIED
** and the new term is marked with TERM_DYNAMIC (because it's pExpr
** needs to be freed with the WhereClause) and TERM_VIRTUAL (because it
** is a commuted copy of a prior term.)  The original term has nChild=1
** and the copy has idxParent set to the index of the original term.
*/
    static void exprAnalyze(
    SrcList pSrc,            /* the FROM clause */
    WhereClause pWC,         /* the WHERE clause */
    int idxTerm               /* Index of the term to be analyzed */
    )
    {
      WhereTerm pTerm;                 /* The term to be analyzed */
      WhereMaskSet pMaskSet;           /* Set of table index masks */
      Expr pExpr;                      /* The expression to be analyzed */
      Bitmask prereqLeft;              /* Prerequesites of the pExpr.pLeft */
      Bitmask prereqAll;               /* Prerequesites of pExpr */
      Bitmask extraRight = 0;           /* Extra dependencies on LEFT JOIN */
      Expr pStr1 = null;               /* RHS of LIKE/GLOB operator */
      bool isComplete = false;         /* RHS of LIKE/GLOB ends with wildcard */
      bool noCase = false;             /* LIKE/GLOB distinguishes case */
      int op;                          /* Top-level operator.  pExpr.op */
      Parse pParse = pWC.pParse;       /* Parsing context */
      sqlite3 db = pParse.db;          /* Data_base connection */

      //if ( db.mallocFailed != 0 )
      //{
      //  return;
      //}
      pTerm = pWC.a[idxTerm];
      pMaskSet = pWC.pMaskSet;
      pExpr = pTerm.pExpr;
      prereqLeft = exprTableUsage( pMaskSet, pExpr.pLeft );
      op = pExpr.op;
      if ( op == TK_IN )
      {
        Debug.Assert( pExpr.pRight == null );
        if ( ExprHasProperty( pExpr, EP_xIsSelect ) )
        {
          pTerm.prereqRight = exprSelectTableUsage( pMaskSet, pExpr.x.pSelect );
        }
        else
        {
          pTerm.prereqRight = exprListTableUsage( pMaskSet, pExpr.x.pList );
        }
      }
      else if ( op == TK_ISNULL )
      {
        pTerm.prereqRight = 0;
      }
      else
      {
        pTerm.prereqRight = exprTableUsage( pMaskSet, pExpr.pRight );
      }
      prereqAll = exprTableUsage( pMaskSet, pExpr );
      if ( ExprHasProperty( pExpr, EP_FromJoin ) )
      {
        Bitmask x = getMask( pMaskSet, pExpr.iRightJoinTable );
        prereqAll |= x;
        extraRight = x - 1;  /* ON clause terms may not be used with an index
** on left table of a LEFT JOIN.  Ticket #3015 */
      }
      pTerm.prereqAll = prereqAll;
      pTerm.leftCursor = -1;
      pTerm.iParent = -1;
      pTerm.eOperator = 0;
      if ( allowedOp( op ) && ( pTerm.prereqRight & prereqLeft ) == 0 )
      {
        Expr pLeft = pExpr.pLeft;
        Expr pRight = pExpr.pRight;
        if ( pLeft.op == TK_COLUMN )
        {
          pTerm.leftCursor = pLeft.iTable;
          pTerm.u.leftColumn = pLeft.iColumn;
          pTerm.eOperator = operatorMask( op );
        }
        if ( pRight != null && pRight.op == TK_COLUMN )
        {
          WhereTerm pNew;
          Expr pDup;
          if ( pTerm.leftCursor >= 0 )
          {
            int idxNew;
            pDup = sqlite3ExprDup( db, pExpr, 0 );
            //if ( db.mallocFailed != 0 )
            //{
            //  sqlite3ExprDelete( db, ref pDup );
            //  return;
            //}
            idxNew = whereClauseInsert( pWC, pDup, TERM_VIRTUAL | TERM_DYNAMIC );
            if ( idxNew == 0 )
              return;
            pNew = pWC.a[idxNew];
            pNew.iParent = idxTerm;
            pTerm = pWC.a[idxTerm];
            pTerm.nChild = 1;
            pTerm.wtFlags |= TERM_COPIED;
          }
          else
          {
            pDup = pExpr;
            pNew = pTerm;
          }
          exprCommute( pParse, pDup );
          pLeft = pDup.pLeft;
          pNew.leftCursor = pLeft.iTable;
          pNew.u.leftColumn = pLeft.iColumn;
          testcase( ( prereqLeft | extraRight ) != prereqLeft );
          pNew.prereqRight = prereqLeft | extraRight;
          pNew.prereqAll = prereqAll;
          pNew.eOperator = operatorMask( pDup.op );
        }
      }

#if  !SQLITE_OMIT_BETWEEN_OPTIMIZATION
      /* If a term is the BETWEEN operator, create two new virtual terms
** that define the range that the BETWEEN implements.  For example:
**
**      a BETWEEN b AND c
**
** is converted into:
**
**      (a BETWEEN b AND c) AND (a>=b) AND (a<=c)
**
** The two new terms are added onto the end of the WhereClause object.
** The new terms are "dynamic" and are children of the original BETWEEN
** term.  That means that if the BETWEEN term is coded, the children are
** skipped.  Or, if the children are satisfied by an index, the original
** BETWEEN term is skipped.
*/
      else if ( pExpr.op == TK_BETWEEN && pWC.op == TK_AND )
      {
        ExprList pList = pExpr.x.pList;
        int i;
        u8[] ops = new u8[] { TK_GE, TK_LE };
        Debug.Assert( pList != null );
        Debug.Assert( pList.nExpr == 2 );
        for ( i = 0; i < 2; i++ )
        {
          Expr pNewExpr;
          int idxNew;
          pNewExpr = sqlite3PExpr( pParse, ops[i],
          sqlite3ExprDup( db, pExpr.pLeft, 0 ),
          sqlite3ExprDup( db, pList.a[i].pExpr, 0 ), null );
          idxNew = whereClauseInsert( pWC, pNewExpr, TERM_VIRTUAL | TERM_DYNAMIC );
          testcase( idxNew == 0 );
          exprAnalyze( pSrc, pWC, idxNew );
          pTerm = pWC.a[idxTerm];
          pWC.a[idxNew].iParent = idxTerm;
        }
        pTerm.nChild = 2;
      }
#endif //* SQLITE_OMIT_BETWEEN_OPTIMIZATION */

#if  !(SQLITE_OMIT_OR_OPTIMIZATION) && !(SQLITE_OMIT_SUBQUERY)
      /* Analyze a term that is composed of two or more subterms connected by
** an OR operator.
*/
      else if ( pExpr.op == TK_OR )
      {
        Debug.Assert( pWC.op == TK_AND );
        exprAnalyzeOrTerm( pSrc, pWC, idxTerm );
        pTerm = pWC.a[idxTerm];
      }
#endif //* SQLITE_OMIT_OR_OPTIMIZATION */

#if  !SQLITE_OMIT_LIKE_OPTIMIZATION
      /* Add constraints to reduce the search space on a LIKE or GLOB
** operator.
**
** A like pattern of the form "x LIKE 'abc%'" is changed into constraints
**
**          x>='abc' AND x<'abd' AND x LIKE 'abc%'
**
** The last character of the prefix "abc" is incremented to form the
** termination condition "abd".
*/
      if ( pWC.op == TK_AND
      && isLikeOrGlob( pParse, pExpr, ref pStr1, ref isComplete, ref noCase ) != 0
      )
      {
        Expr pLeft;       /* LHS of LIKE/GLOB operator */
        Expr pStr2;       /* Copy of pStr1 - RHS of LIKE/GLOB operator */
        Expr pNewExpr1;
        Expr pNewExpr2;
        int idxNew1;
        int idxNew2;
        CollSeq pColl;    /* Collating sequence to use */

        pLeft = pExpr.x.pList.a[1].pExpr;
        pStr2 = sqlite3ExprDup( db, pStr1, 0 );
        ////if ( 0 == db.mallocFailed )
        {
          int c, pC;    /* Last character before the first wildcard */
          pC = pStr2.u.zToken[sqlite3Strlen30( pStr2.u.zToken ) - 1];
          c = pC;
          if ( noCase )
          {
            /* The point is to increment the last character before the first
            ** wildcard.  But if we increment '@', that will push it into the
            ** alphabetic range where case conversions will mess up the
            ** inequality.  To avoid this, make sure to also run the full
            ** LIKE on all candidate expressions by clearing the isComplete flag
            */
            if ( c == 'A' - 1 )
              isComplete = false;   /* EV: R-64339-08207 */
            c = sqlite3UpperToLower[c];
          }
          pStr2.u.zToken = pStr2.u.zToken.Substring( 0, sqlite3Strlen30( pStr2.u.zToken ) - 1 ) + (char)( c + 1 );// pC = c + 1;
        }
        pColl = sqlite3FindCollSeq( db, SQLITE_UTF8, noCase ? "NOCASE" : "BINARY", 0 );
        pNewExpr1 = sqlite3PExpr( pParse, TK_GE,
        sqlite3ExprSetColl( sqlite3ExprDup( db, pLeft, 0 ), pColl ),
        pStr1, 0 );
        idxNew1 = whereClauseInsert( pWC, pNewExpr1, TERM_VIRTUAL | TERM_DYNAMIC );
        testcase( idxNew1 == 0 );
        exprAnalyze( pSrc, pWC, idxNew1 );
        pNewExpr2 = sqlite3PExpr( pParse, TK_LT,
                 sqlite3ExprSetColl( sqlite3ExprDup( db, pLeft, 0 ), pColl ),
                 pStr2, null );
        idxNew2 = whereClauseInsert( pWC, pNewExpr2, TERM_VIRTUAL | TERM_DYNAMIC );
        testcase( idxNew2 == 0 );
        exprAnalyze( pSrc, pWC, idxNew2 );
        pTerm = pWC.a[idxTerm];
        if ( isComplete )
        {
          pWC.a[idxNew1].iParent = idxTerm;
          pWC.a[idxNew2].iParent = idxTerm;
          pTerm.nChild = 2;
        }
      }
#endif //* SQLITE_OMIT_LIKE_OPTIMIZATION */

#if  !SQLITE_OMIT_VIRTUALTABLE
/* Add a WO_MATCH auxiliary term to the constraint set if the
** current expression is of the form:  column MATCH expr.
** This information is used by the xBestIndex methods of
** virtual tables.  The native query optimizer does not attempt
** to do anything with MATCH functions.
*/
      if ( isMatchOfColumn( pExpr ) != 0 )
      {
        int idxNew;
        Expr pRight, pLeft;
        WhereTerm pNewTerm;
        Bitmask prereqColumn, prereqExpr;

        pRight = pExpr.x.pList.a[0].pExpr;
        pLeft = pExpr.x.pList.a[1].pExpr;
        prereqExpr = exprTableUsage( pMaskSet, pRight );
        prereqColumn = exprTableUsage( pMaskSet, pLeft );
        if ( ( prereqExpr & prereqColumn ) == 0 )
        {
          Expr pNewExpr;
          pNewExpr = sqlite3PExpr( pParse, TK_MATCH,
          null, sqlite3ExprDup( db, pRight, 0 ), null );
          idxNew = whereClauseInsert( pWC, pNewExpr, TERM_VIRTUAL | TERM_DYNAMIC );
          testcase( idxNew == 0 );
          pNewTerm = pWC.a[idxNew];
          pNewTerm.prereqRight = prereqExpr;
          pNewTerm.leftCursor = pLeft.iTable;
          pNewTerm.u.leftColumn = pLeft.iColumn;
          pNewTerm.eOperator = WO_MATCH;
          pNewTerm.iParent = idxTerm;
          pTerm = pWC.a[idxTerm];
          pTerm.nChild = 1;
          pTerm.wtFlags |= TERM_COPIED;
          pNewTerm.prereqAll = pTerm.prereqAll;
        }
}
#endif //* SQLITE_OMIT_VIRTUALTABLE */

#if SQLITE_ENABLE_STAT2
      /* When sqlite_stat2 histogram data is available an operator of the
  ** form "x IS NOT NULL" can sometimes be evaluated more efficiently
  ** as "x>NULL" if x is not an INTEGER PRIMARY KEY.  So construct a
  ** virtual term of that form.
  **
  ** Note that the virtual term must be tagged with TERM_VNULL.  This
  ** TERM_VNULL tag will suppress the not-null check at the beginning
  ** of the loop.  Without the TERM_VNULL flag, the not-null check at
  ** the start of the loop will prevent any results from being returned.
  */
      if ( pExpr.op == TK_NOTNULL
       && pExpr.pLeft.op == TK_COLUMN
       && pExpr.pLeft.iColumn >= 0
      )
      {
        Expr pNewExpr;
        Expr pLeft = pExpr.pLeft;
        int idxNew;
        WhereTerm pNewTerm;

        pNewExpr = sqlite3PExpr( pParse, TK_GT,
                                sqlite3ExprDup( db, pLeft, 0 ),
                                sqlite3PExpr( pParse, TK_NULL, 0, 0, 0 ), 0 );

        idxNew = whereClauseInsert( pWC, pNewExpr,
                                  TERM_VIRTUAL | TERM_DYNAMIC | TERM_VNULL );
        if ( idxNew != 0 )
        {
          pNewTerm = pWC.a[idxNew];
          pNewTerm.prereqRight = 0;
          pNewTerm.leftCursor = pLeft.iTable;
          pNewTerm.u.leftColumn = pLeft.iColumn;
          pNewTerm.eOperator = WO_GT;
          pNewTerm.iParent = idxTerm;
          pTerm = pWC.a[idxTerm];
          pTerm.nChild = 1;
          pTerm.wtFlags |= TERM_COPIED;
          pNewTerm.prereqAll = pTerm.prereqAll;
        }
      }
#endif //* SQLITE_ENABLE_STAT2 */

      /* Prevent ON clause terms of a LEFT JOIN from being used to drive
** an index for tables to the left of the join.
*/
      pTerm.prereqRight |= extraRight;
    }

    /*
    ** Return TRUE if any of the expressions in pList.a[iFirst...] contain
    ** a reference to any table other than the iBase table.
    */
    static bool referencesOtherTables(
    ExprList pList,          /* Search expressions in ths list */
    WhereMaskSet pMaskSet,   /* Mapping from tables to bitmaps */
    int iFirst,               /* Be searching with the iFirst-th expression */
    int iBase                 /* Ignore references to this table */
    )
    {
      Bitmask allowed = ~getMask( pMaskSet, iBase );
      while ( iFirst < pList.nExpr )
      {
        if ( ( exprTableUsage( pMaskSet, pList.a[iFirst++].pExpr ) & allowed ) != 0 )
        {
          return true;
        }
      }
      return false;
    }


    /*
    ** This routine decides if pIdx can be used to satisfy the ORDER BY
    ** clause.  If it can, it returns 1.  If pIdx cannot satisfy the
    ** ORDER BY clause, this routine returns 0.
    **
    ** pOrderBy is an ORDER BY clause from a SELECT statement.  pTab is the
    ** left-most table in the FROM clause of that same SELECT statement and
    ** the table has a cursor number of "_base".  pIdx is an index on pTab.
    **
    ** nEqCol is the number of columns of pIdx that are used as equality
    ** constraints.  Any of these columns may be missing from the ORDER BY
    ** clause and the match can still be a success.
    **
    ** All terms of the ORDER BY that match against the index must be either
    ** ASC or DESC.  (Terms of the ORDER BY clause past the end of a UNIQUE
    ** index do not need to satisfy this constraint.)  The pbRev value is
    ** set to 1 if the ORDER BY clause is all DESC and it is set to 0 if
    ** the ORDER BY clause is all ASC.
    */
    static bool isSortingIndex(
    Parse pParse,           /* Parsing context */
    WhereMaskSet pMaskSet,  /* Mapping from table cursor numbers to bitmaps */
    Index pIdx,             /* The index we are testing */
    int _base,              /* Cursor number for the table to be sorted */
    ExprList pOrderBy,      /* The ORDER BY clause */
    int nEqCol,             /* Number of index columns with == constraints */
    int wsFlags,            /* Index usages flags */
    ref int pbRev           /* Set to 1 if ORDER BY is DESC */
    )
    {
      int i, j;                       /* Loop counters */
      int sortOrder = 0;              /* XOR of index and ORDER BY sort direction */
      int nTerm;                      /* Number of ORDER BY terms */
      ExprList_item pTerm;            /* A term of the ORDER BY clause */
      sqlite3 db = pParse.db;

      Debug.Assert( pOrderBy != null );
      nTerm = pOrderBy.nExpr;
      Debug.Assert( nTerm > 0 );

      /* Argument pIdx must either point to a 'real' named index structure, 
      ** or an index structure allocated on the stack by bestBtreeIndex() to
      ** represent the rowid index that is part of every table.  */
      Debug.Assert( !string.IsNullOrEmpty( pIdx.zName ) || ( pIdx.nColumn == 1 && pIdx.aiColumn[0] == -1 ) );

      /* Match terms of the ORDER BY clause against columns of
      ** the index.
      **
      ** Note that indices have pIdx.nColumn regular columns plus
      ** one additional column containing the rowid.  The rowid column
      ** of the index is also allowed to match against the ORDER BY
      ** clause.
      */
      for ( i = j = 0; j < nTerm && i <= pIdx.nColumn; i++ )
      {
        pTerm = pOrderBy.a[j];
        Expr pExpr;        /* The expression of the ORDER BY pTerm */
        CollSeq pColl;     /* The collating sequence of pExpr */
        int termSortOrder; /* Sort order for this term */
        int iColumn;       /* The i-th column of the index.  -1 for rowid */
        int iSortOrder;    /* 1 for DESC, 0 for ASC on the i-th index term */
        string zColl;      /* Name of the collating sequence for i-th index term */

        pExpr = pTerm.pExpr;
        if ( pExpr.op != TK_COLUMN || pExpr.iTable != _base )
        {
          /* Can not use an index sort on anything that is not a column in the
          ** left-most table of the FROM clause */
          break;
        }
        pColl = sqlite3ExprCollSeq( pParse, pExpr );
        if ( null == pColl )
        {
          pColl = db.pDfltColl;
        }
        if ( !string.IsNullOrEmpty( pIdx.zName ) && i < pIdx.nColumn )
        {
          iColumn = pIdx.aiColumn[i];
          if ( iColumn == pIdx.pTable.iPKey )
          {
            iColumn = -1;
          }
          iSortOrder = pIdx.aSortOrder[i];
          zColl = pIdx.azColl[i];
        }
        else
        {
          iColumn = -1;
          iSortOrder = 0;
          zColl = pColl.zName;
        }
        if ( pExpr.iColumn != iColumn || !pColl.zName.Equals( zColl, StringComparison.OrdinalIgnoreCase ) )
        {
          /* Term j of the ORDER BY clause does not match column i of the index */
          if ( i < nEqCol )
          {
            /* If an index column that is constrained by == fails to match an
            ** ORDER BY term, that is OK.  Just ignore that column of the index
            */
            continue;
          }
          else if ( i == pIdx.nColumn )
          {
            /* Index column i is the rowid.  All other terms match. */
            break;
          }
          else
          {
            /* If an index column fails to match and is not constrained by ==
            ** then the index cannot satisfy the ORDER BY constraint.
            */
            return false;
          }
        }
        Debug.Assert( pIdx.aSortOrder != null || iColumn == -1 );
        Debug.Assert( pTerm.sortOrder == 0 || pTerm.sortOrder == 1 );
        Debug.Assert( iSortOrder == 0 || iSortOrder == 1 );
        termSortOrder = iSortOrder ^ pTerm.sortOrder;
        if ( i > nEqCol )
        {
          if ( termSortOrder != sortOrder )
          {
            /* Indices can only be used if all ORDER BY terms past the
            ** equality constraints are all either DESC or ASC. */
            return false;
          }
        }
        else
        {
          sortOrder = termSortOrder;
        }
        j++;
        //pTerm++;
        if ( iColumn < 0 && !referencesOtherTables( pOrderBy, pMaskSet, j, _base ) )
        {
          /* If the indexed column is the primary key and everything matches
          ** so far and none of the ORDER BY terms to the right reference other
          ** tables in the join, then we are Debug.Assured that the index can be used
          ** to sort because the primary key is unique and so none of the other
          ** columns will make any difference
          */
          j = nTerm;
        }
      }

      pbRev = sortOrder != 0 ? 1 : 0;
      if ( j >= nTerm )
      {
        /* All terms of the ORDER BY clause are covered by this index so
        ** this index can be used for sorting. */
        return true;
      }
      if ( pIdx.onError != OE_None && i == pIdx.nColumn
        && ( wsFlags & WHERE_COLUMN_NULL ) == 0
        && !referencesOtherTables( pOrderBy, pMaskSet, j, _base ) )
      {
        /* All terms of this index match some prefix of the ORDER BY clause
        ** and the index is UNIQUE and no terms on the tail of the ORDER BY
        ** clause reference other tables in a join.  If this is all true then
        ** the order by clause is superfluous.  Not that if the matching
        ** condition is IS NULL then the result is not necessarily unique
        ** even on a UNIQUE index, so disallow those cases. */
        return true;
      }
      return false;
    }

    /*
    ** Prepare a crude estimate of the logarithm of the input value.
    ** The results need not be exact.  This is only used for estimating
    ** the total cost of performing operations with O(logN) or O(NlogN)
    ** complexity.  Because N is just a guess, it is no great tragedy if
    ** logN is a little off.
    */
    static double estLog( double N )
    {
      double logN = 1;
      double x = 10;
      while ( N > x )
      {
        logN += 1;
        x *= 10;
      }
      return logN;
    }

    /*
    ** Two routines for printing the content of an sqlite3_index_info
    ** structure.  Used for testing and debugging only.  If neither
    ** SQLITE_TEST or SQLITE_DEBUG are defined, then these routines
    ** are no-ops.
    */
#if  !(SQLITE_OMIT_VIRTUALTABLE) && (SQLITE_DEBUG)
static void TRACE_IDX_INPUTS( sqlite3_index_info p )
{
int i;
if ( !sqlite3WhereTrace ) return;
for ( i = 0 ; i < p.nConstraint ; i++ )
{
sqlite3DebugPrintf( "  constraint[%d]: col=%d termid=%d op=%d usabled=%d\n",
i,
p.aConstraint[i].iColumn,
p.aConstraint[i].iTermOffset,
p.aConstraint[i].op,
p.aConstraint[i].usable );
}
for ( i = 0 ; i < p.nOrderBy ; i++ )
{
sqlite3DebugPrintf( "  orderby[%d]: col=%d desc=%d\n",
i,
p.aOrderBy[i].iColumn,
p.aOrderBy[i].desc );
}
}
static void TRACE_IDX_OUTPUTS( sqlite3_index_info p )
{
int i;
if ( !sqlite3WhereTrace ) return;
for ( i = 0 ; i < p.nConstraint ; i++ )
{
sqlite3DebugPrintf( "  usage[%d]: argvIdx=%d omit=%d\n",
i,
p.aConstraintUsage[i].argvIndex,
p.aConstraintUsage[i].omit );
}
sqlite3DebugPrintf( "  idxNum=%d\n", p.idxNum );
sqlite3DebugPrintf( "  idxStr=%s\n", p.idxStr );
sqlite3DebugPrintf( "  orderByConsumed=%d\n", p.orderByConsumed );
sqlite3DebugPrintf( "  estimatedCost=%g\n", p.estimatedCost );
}
#else
    //#define TRACE_IDX_INPUTS(A)
    static void TRACE_IDX_INPUTS( sqlite3_index_info p ) { }
    //#define TRACE_IDX_OUTPUTS(A)
    static void TRACE_IDX_OUTPUTS( sqlite3_index_info p ) { }
#endif

    /*
** Required because bestIndex() is called by bestOrClauseIndex()
*/
    //static void bestIndex(
    //Parse*, WhereClause*, struct SrcList_item*, 
    //Bitmask, ExprList*, WhereCost);

    /*
    ** This routine attempts to find an scanning strategy that can be used
    ** to optimize an 'OR' expression that is part of a WHERE clause.
    **
    ** The table associated with FROM clause term pSrc may be either a
    ** regular B-Tree table or a virtual table.
    */
    static void bestOrClauseIndex(
    Parse pParse,               /* The parsing context */
    WhereClause pWC,            /* The WHERE clause */
    SrcList_item pSrc,          /* The FROM clause term to search */
    Bitmask notReady,           /* Mask of cursors not available for indexing */
    Bitmask notValid,           /* Cursors not available for any purpose */
    ExprList pOrderBy,          /* The ORDER BY clause */
    WhereCost pCost             /* Lowest cost query plan */
    )
    {
#if !SQLITE_OMIT_OR_OPTIMIZATION
      int iCur = pSrc.iCursor;   /* The cursor of the table to be accessed */
      Bitmask maskSrc = getMask( pWC.pMaskSet, iCur );  /* Bitmask for pSrc */
      ////WhereTerm pWCEnd = pWC.a[pWC.nTerm];        /* End of pWC.a[] */
      WhereTerm pTerm;                 /* A single term of the WHERE clause */

      /* No OR-clause optimization allowed if the INDEXED BY or NOT INDEXED clauses
      ** are used */
      if ( pSrc.notIndexed != 0 || pSrc.pIndex != null )
      {
        return;
      }

      /* Search the WHERE clause terms for a usable WO_OR term. */
      for ( int _pt = 0; _pt < pWC.nTerm; _pt++ )//<pWCEnd; pTerm++)
      {
        pTerm = pWC.a[_pt];
        if ( pTerm.eOperator == WO_OR
        && ( ( pTerm.prereqAll & ~maskSrc ) & notReady ) == 0
        && ( pTerm.u.pOrInfo.indexable & maskSrc ) != 0
        )
        {
          WhereClause pOrWC = pTerm.u.pOrInfo.wc;
          ////WhereTerm pOrWCEnd = pOrWC.a[pOrWC.nTerm];
          WhereTerm pOrTerm;
          int flags = WHERE_MULTI_OR;
          double rTotal = 0;
          double nRow = 0;
          Bitmask used = 0;

          for ( int _pOrWC = 0; _pOrWC < pOrWC.nTerm; _pOrWC++ )//pOrTerm = pOrWC.a ; pOrTerm < pOrWCEnd ; pOrTerm++ )
          {
            pOrTerm = pOrWC.a[_pOrWC];
            WhereCost sTermCost = null;
#if  (SQLITE_TEST) && (SQLITE_DEBUG)
            WHERETRACE( "... Multi-index OR testing for term %d of %d....\n",
            _pOrWC, pOrWC.nTerm - _pOrWC//( pOrTerm - pOrWC.a ), ( pTerm - pWC.a )
            );
#endif
            if ( pOrTerm.eOperator == WO_AND )
            {
              WhereClause pAndWC = pOrTerm.u.pAndInfo.wc;
              bestIndex( pParse, pAndWC, pSrc, notReady, notValid, null, ref sTermCost );
            }
            else if ( pOrTerm.leftCursor == iCur )
            {
              WhereClause tempWC = new WhereClause();
              tempWC.pParse = pWC.pParse;
              tempWC.pMaskSet = pWC.pMaskSet;
              tempWC.op = TK_AND;
              tempWC.a = new WhereTerm[2];
              tempWC.a[0] = pOrTerm;
              tempWC.nTerm = 1;
              bestIndex( pParse, tempWC, pSrc, notReady, notValid, null, ref sTermCost );
            }
            else
            {
              continue;
            }
            rTotal += sTermCost.rCost;
            nRow += sTermCost.plan.nRow;
            used |= sTermCost.used;
            if ( rTotal >= pCost.rCost )
              break;
          }

          /* If there is an ORDER BY clause, increase the scan cost to account
          ** for the cost of the sort. */
          if ( pOrderBy != null )
          {
#if  (SQLITE_TEST) && (SQLITE_DEBUG)
            WHERETRACE( "... sorting increases OR cost %.9g to %.9g\n",
            rTotal, rTotal + nRow * estLog( nRow ) );
#endif
            rTotal += nRow * estLog( nRow );
          }

          /* If the cost of scanning using this OR term for optimization is
          ** less than the current cost stored in pCost, replace the contents
          ** of pCost. */
#if  (SQLITE_TEST) && (SQLITE_DEBUG)
          WHERETRACE( "... multi-index OR cost=%.9g nrow=%.9g\n", rTotal, nRow );
#endif
          if ( rTotal < pCost.rCost )
          {
            pCost.rCost = rTotal;
            pCost.used = used;
            pCost.plan.nRow = nRow;
            pCost.plan.wsFlags = (uint)flags;
            pCost.plan.u.pTerm = pTerm;
          }
        }
      }
#endif //* SQLITE_OMIT_OR_OPTIMIZATION */
    }

#if !SQLITE_OMIT_AUTOMATIC_INDEX
    /*
** Return TRUE if the WHERE clause term pTerm is of a form where it
** could be used with an index to access pSrc, assuming an appropriate
** index existed.
*/
    static int termCanDriveIndex(
    WhereTerm pTerm,              /* WHERE clause term to check */
    SrcList_item pSrc,     /* Table we are trying to access */
    Bitmask notReady               /* Tables in outer loops of the join */
    )
    {
      char aff;
      if ( pTerm.leftCursor != pSrc.iCursor )
        return 0;
      if ( pTerm.eOperator != WO_EQ )
        return 0;
      if ( ( pTerm.prereqRight & notReady ) != 0 )
        return 0;
      aff = pSrc.pTab.aCol[pTerm.u.leftColumn].affinity;
      if ( !sqlite3IndexAffinityOk( pTerm.pExpr, aff ) )
        return 0;
      return 1;
    }
#endif

#if !SQLITE_OMIT_AUTOMATIC_INDEX
    /*
** If the query plan for pSrc specified in pCost is a full table scan
** and indexing is allows (if there is no NOT INDEXED clause) and it
** possible to construct a transient index that would perform better
** than a full table scan even when the cost of constructing the index
** is taken into account, then alter the query plan to use the
** transient index.
*/
    static void bestAutomaticIndex(
    Parse pParse,              /* The parsing context */
    WhereClause pWC,           /* The WHERE clause */
    SrcList_item pSrc,         /* The FROM clause term to search */
    Bitmask notReady,          /* Mask of cursors that are not available */
    WhereCost pCost            /* Lowest cost query plan */
    )
    {
      double nTableRow;          /* Rows in the input table */
      double logN;               /* log(nTableRow) */
      double costTempIdx;        /* per-query cost of the transient index */
      WhereTerm pTerm;           /* A single term of the WHERE clause */
      WhereTerm pWCEnd;          /* End of pWC.a[] */
      Table pTable;              /* Table that might be indexed */

      if ( pParse.nQueryLoop <= (double)1 )
      {
        /* There is no point in building an automatic index for a single scan */
        return;
      }
      if ( ( pParse.db.flags & SQLITE_AutoIndex ) == 0 )
      {
        /* Automatic indices are disabled at run-time */
        return;
      }
      if ( ( pCost.plan.wsFlags & WHERE_NOT_FULLSCAN ) != 0 )
      {
        /* We already have some kind of index in use for this query. */
        return;
      }
      if ( pSrc.notIndexed != 0 )
      {
        /* The NOT INDEXED clause appears in the SQL. */
        return;
      }

      Debug.Assert( pParse.nQueryLoop >= (double)1 );
      pTable = pSrc.pTab;
      nTableRow = pTable.nRowEst;
      logN = estLog( nTableRow );
      costTempIdx = 2 * logN * ( nTableRow / pParse.nQueryLoop + 1 );
      if ( costTempIdx >= pCost.rCost )
      {
        /* The cost of creating the transient table would be greater than
        ** doing the full table scan */
        return;
      }

      /* Search for any equality comparison term */
      //pWCEnd = pWC.a[pWC.nTerm];
      for ( int ipTerm = 0; ipTerm < pWC.nTerm; ipTerm++ )//; pTerm<pWCEnd; pTerm++)
      {
        pTerm = pWC.a[ipTerm];
        if ( termCanDriveIndex( pTerm, pSrc, notReady ) != 0 )
        {
#if  (SQLITE_TEST) && (SQLITE_DEBUG)
          WHERETRACE( "auto-index reduces cost from %.2f to %.2f\n",
          pCost.rCost, costTempIdx );
#endif
          pCost.rCost = costTempIdx;
          pCost.plan.nRow = logN + 1;
          pCost.plan.wsFlags = WHERE_TEMP_INDEX;
          pCost.used = pTerm.prereqRight;
          break;
        }
      }
    }
#else
//# define bestAutomaticIndex(A,B,C,D,E)  /* no-op */
static void bestAutomaticIndex(
Parse pParse,              /* The parsing context */
WhereClause pWC,           /* The WHERE clause */
SrcList_item pSrc,         /* The FROM clause term to search */
Bitmask notReady,          /* Mask of cursors that are not available */
WhereCost pCost            /* Lowest cost query plan */
){}
#endif //* SQLITE_OMIT_AUTOMATIC_INDEX */


#if !SQLITE_OMIT_AUTOMATIC_INDEX
    /*
** Generate code to construct the Index object for an automatic index
** and to set up the WhereLevel object pLevel so that the code generator
** makes use of the automatic index.
*/
    static void constructAutomaticIndex(
    Parse pParse,              /* The parsing context */
    WhereClause pWC,           /* The WHERE clause */
    SrcList_item pSrc,         /* The FROM clause term to get the next index */
    Bitmask notReady,          /* Mask of cursors that are not available */
    WhereLevel pLevel          /* Write new index here */
    )
    {
      int nColumn;               /* Number of columns in the constructed index */
      WhereTerm pTerm;           /* A single term of the WHERE clause */
      WhereTerm pWCEnd;          /* End of pWC.a[] */
      int nByte;                 /* Byte of memory needed for pIdx */
      Index pIdx;                /* Object describing the transient index */
      Vdbe v;                    /* Prepared statement under construction */
      int regIsInit;             /* Register set by initialization */
      int addrInit;              /* Address of the initialization bypass jump */
      Table pTable;              /* The table being indexed */
      KeyInfo pKeyinfo;          /* Key information for the index */
      int addrTop;               /* Top of the index fill loop */
      int regRecord;             /* Register holding an index record */
      int n;                     /* Column counter */
      int i;                     /* Loop counter */
      int mxBitCol;              /* Maximum column in pSrc.colUsed */
      CollSeq pColl;             /* Collating sequence to on a column */
      Bitmask idxCols;           /* Bitmap of columns used for indexing */
      Bitmask extraCols;         /* Bitmap of additional columns */

      /* Generate code to skip over the creation and initialization of the
      ** transient index on 2nd and subsequent iterations of the loop. */
      v = pParse.pVdbe;
      Debug.Assert( v != null );
      regIsInit = ++pParse.nMem;
      addrInit = sqlite3VdbeAddOp1( v, OP_If, regIsInit );
      sqlite3VdbeAddOp2( v, OP_Integer, 1, regIsInit );

      /* Count the number of columns that will be added to the index
      ** and used to match WHERE clause constraints */
      nColumn = 0;
      pTable = pSrc.pTab;
      //pWCEnd = pWC.a[pWC.nTerm];
      idxCols = 0;
      for ( int ipTerm = 0; ipTerm < pWC.nTerm; ipTerm++ )//; pTerm<pWCEnd; pTerm++)
      {
        pTerm = pWC.a[ipTerm];
        if ( termCanDriveIndex( pTerm, pSrc, notReady ) != 0 )
        {
          int iCol = pTerm.u.leftColumn;
          Bitmask cMask = iCol >= BMS ? ( (Bitmask)1 ) << ( BMS - 1 ) : ( (Bitmask)1 ) << iCol;
          testcase( iCol == BMS );
          testcase( iCol == BMS - 1 );
          if ( ( idxCols & cMask ) == 0 )
          {
            nColumn++;
            idxCols |= cMask;
          }
        }
      }
      Debug.Assert( nColumn > 0 );
      pLevel.plan.nEq = (u32)nColumn;

      /* Count the number of additional columns needed to create a
      ** covering index.  A "covering index" is an index that contains all
      ** columns that are needed by the query.  With a covering index, the
      ** original table never needs to be accessed.  Automatic indices must
      ** be a covering index because the index will not be updated if the
      ** original table changes and the index and table cannot both be used
      ** if they go out of sync.
      */
      extraCols = pSrc.colUsed & ( ~idxCols | ( ( (Bitmask)1 ) << ( BMS - 1 ) ) );
      mxBitCol = ( pTable.nCol >= BMS - 1 ) ? BMS - 1 : pTable.nCol;
      testcase( pTable.nCol == BMS - 1 );
      testcase( pTable.nCol == BMS - 2 );
      for ( i = 0; i < mxBitCol; i++ )
      {
        if ( ( extraCols & ( ( (Bitmask)1 ) << i ) ) != 0 )
          nColumn++;
      }
      if ( ( pSrc.colUsed & ( ( (Bitmask)1 ) << ( BMS - 1 ) ) ) != 0 )
      {
        nColumn += pTable.nCol - BMS + 1;
      }
      pLevel.plan.wsFlags |= WHERE_COLUMN_EQ | WHERE_IDX_ONLY | WO_EQ;

      /* Construct the Index object to describe this index */
      //nByte = sizeof(Index);
      //nByte += nColumn*sizeof(int);     /* Index.aiColumn */
      //nByte += nColumn*sizeof(char);   /* Index.azColl */
      //nByte += nColumn;                 /* Index.aSortOrder */
      //pIdx = sqlite3DbMallocZero(pParse.db, nByte);
      //if( pIdx==null) return;
      pIdx = new Index();
      pLevel.plan.u.pIdx = pIdx;
      pIdx.azColl = new string[nColumn + 1];// pIdx[1];
      pIdx.aiColumn = new int[nColumn + 1];// pIdx.azColl[nColumn];
      pIdx.aSortOrder = new u8[nColumn + 1];// pIdx.aiColumn[nColumn];
      pIdx.zName = "auto-index";
      pIdx.nColumn = nColumn;
      pIdx.pTable = pTable;
      n = 0;
      idxCols = 0;
      //for(pTerm=pWC.a; pTerm<pWCEnd; pTerm++){
      for ( int ipTerm = 0; ipTerm < pWC.nTerm; ipTerm++ )
      {
        pTerm = pWC.a[ipTerm];
        if ( termCanDriveIndex( pTerm, pSrc, notReady ) != 0 )
        {
          int iCol = pTerm.u.leftColumn;
          Bitmask cMask = iCol >= BMS ? ( (Bitmask)1 ) << ( BMS - 1 ) : ( (Bitmask)1 ) << iCol;
          if ( ( idxCols & cMask ) == 0 )
          {
            Expr pX = pTerm.pExpr;
            idxCols |= cMask;
            pIdx.aiColumn[n] = pTerm.u.leftColumn;
            pColl = sqlite3BinaryCompareCollSeq( pParse, pX.pLeft, pX.pRight );
            pIdx.azColl[n] = ALWAYS( pColl != null ) ? pColl.zName : "BINARY";
            n++;
          }
        }
      }
      Debug.Assert( (u32)n == pLevel.plan.nEq );

      /* Add additional columns needed to make the automatic index into
      ** a covering index */
      for ( i = 0; i < mxBitCol; i++ )
      {
        if ( ( extraCols & ( ( (Bitmask)1 ) << i ) ) != 0 )
        {
          pIdx.aiColumn[n] = i;
          pIdx.azColl[n] = "BINARY";
          n++;
        }
      }
      if ( ( pSrc.colUsed & ( ( (Bitmask)1 ) << ( BMS - 1 ) ) ) != 0 )
      {
        for ( i = BMS - 1; i < pTable.nCol; i++ )
        {
          pIdx.aiColumn[n] = i;
          pIdx.azColl[n] = "BINARY";
          n++;
        }
      }
      Debug.Assert( n == nColumn );

      /* Create the automatic index */
      pKeyinfo = sqlite3IndexKeyinfo( pParse, pIdx );
      Debug.Assert( pLevel.iIdxCur >= 0 );
      sqlite3VdbeAddOp4( v, OP_OpenAutoindex, pLevel.iIdxCur, nColumn + 1, 0,
      pKeyinfo, P4_KEYINFO_HANDOFF );
      VdbeComment( v, "for %s", pTable.zName );

      /* Fill the automatic index with content */
      addrTop = sqlite3VdbeAddOp1( v, OP_Rewind, pLevel.iTabCur );
      regRecord = sqlite3GetTempReg( pParse );
      sqlite3GenerateIndexKey( pParse, pIdx, pLevel.iTabCur, regRecord, true );
      sqlite3VdbeAddOp2( v, OP_IdxInsert, pLevel.iIdxCur, regRecord );
      sqlite3VdbeChangeP5( v, OPFLAG_USESEEKRESULT );
      sqlite3VdbeAddOp2( v, OP_Next, pLevel.iTabCur, addrTop + 1 );
      sqlite3VdbeChangeP5( v, SQLITE_STMTSTATUS_AUTOINDEX );
      sqlite3VdbeJumpHere( v, addrTop );
      sqlite3ReleaseTempReg( pParse, regRecord );

      /* Jump here when skipping the initialization */
      sqlite3VdbeJumpHere( v, addrInit );
    }
#endif //* SQLITE_OMIT_AUTOMATIC_INDEX */

#if !SQLITE_OMIT_VIRTUALTABLE
    /*
** Allocate and populate an sqlite3_index_info structure. It is the
** responsibility of the caller to eventually release the structure
** by passing the pointer returned by this function to //sqlite3_free().
*/
    static sqlite3_index_info allocateIndexInfo(
    Parse pParse,
    WhereClause pWC,
    SrcList_item pSrc,
    ExprList pOrderBy
    )
    {
      int i, j;
      int nTerm;
      sqlite3_index_constraint[] pIdxCons;
      sqlite3_index_orderby[] pIdxOrderBy;
      sqlite3_index_constraint_usage[] pUsage;
      WhereTerm pTerm;
      int nOrderBy;
      sqlite3_index_info pIdxInfo;

#if  (SQLITE_TEST) && (SQLITE_DEBUG)
      WHERETRACE( "Recomputing index info for %s...\n", pSrc.pTab.zName );
#endif

      /* Count the number of possible WHERE clause constraints referring
** to this virtual table */
      for ( i = nTerm = 0; i < pWC.nTerm; i++)//, pTerm++ )
      {
        pTerm = pWC.a[i];
        if ( pTerm.leftCursor != pSrc.iCursor )
          continue;
        Debug.Assert( ( pTerm.eOperator & ( pTerm.eOperator - 1 ) ) == 0 );
        testcase( pTerm.eOperator == WO_IN );
        testcase( pTerm.eOperator == WO_ISNULL );
        if ( ( pTerm.eOperator & ( WO_IN | WO_ISNULL ) ) != 0 )
          continue;
        nTerm++;
      }

      /* If the ORDER BY clause contains only columns in the current
      ** virtual table then allocate space for the aOrderBy part of
      ** the sqlite3_index_info structure.
      */
      nOrderBy = 0;
      if ( pOrderBy != null )
      {
        for ( i = 0; i < pOrderBy.nExpr; i++ )
        {
          Expr pExpr = pOrderBy.a[i].pExpr;
          if ( pExpr.op != TK_COLUMN || pExpr.iTable != pSrc.iCursor )
            break;
        }
        if ( i == pOrderBy.nExpr )
        {
          nOrderBy = pOrderBy.nExpr;
        }
      }

      /* Allocate the sqlite3_index_info structure
      */
      pIdxInfo = new sqlite3_index_info();
      //sqlite3DbMallocZero(pParse.db, sizeof(*pIdxInfo)
      //+ (sizeof(*pIdxCons) + sizeof(*pUsage))*nTerm
      //+ sizeof(*pIdxOrderBy)*nOrderBy );
      //if ( pIdxInfo == null )
      //{
      //  sqlite3ErrorMsg( pParse, "out of memory" );
      //  /* (double)0 In case of SQLITE_OMIT_FLOATING_POINT... */
      //  return null;
      //}

      /* Initialize the structure.  The sqlite3_index_info structure contains
      ** many fields that are declared "const" to prevent xBestIndex from
      ** changing them.  We have to do some funky casting in order to
      ** initialize those fields.
      */
      pIdxCons = new sqlite3_index_constraint[nTerm];//(sqlite3_index_constraint)pIdxInfo[1];
      pIdxOrderBy = new sqlite3_index_orderby[nOrderBy];//(sqlite3_index_orderby)pIdxCons[nTerm];
      pUsage = new sqlite3_index_constraint_usage[nTerm];//(sqlite3_index_constraint_usage)pIdxOrderBy[nOrderBy];
      pIdxInfo.nConstraint = nTerm;
      pIdxInfo.nOrderBy = nOrderBy;
      pIdxInfo.aConstraint = pIdxCons;
      pIdxInfo.aOrderBy = pIdxOrderBy;
      pIdxInfo.aConstraintUsage =
      pUsage;

      for ( i = j = 0; i < pWC.nTerm; i++)//, pTerm++ )
      {
        pTerm = pWC.a[i];
        if ( pTerm.leftCursor != pSrc.iCursor )
          continue;
        Debug.Assert( ( pTerm.eOperator & ( pTerm.eOperator - 1 ) ) == 0 );
        testcase( pTerm.eOperator == WO_IN );
        testcase( pTerm.eOperator == WO_ISNULL );
        if ( ( pTerm.eOperator & ( WO_IN | WO_ISNULL ) ) != 0 )
          continue;
        if ( pIdxCons[j] == null )
          pIdxCons[j] = new sqlite3_index_constraint();
        pIdxCons[j].iColumn = pTerm.u.leftColumn;
        pIdxCons[j].iTermOffset = i;
        pIdxCons[j].op = (u8)pTerm.eOperator;
        /* The direct Debug.Assignment in the previous line is possible only because
        ** the WO_ and SQLITE_INDEX_CONSTRAINT_ codes are identical.  The
        ** following Debug.Asserts verify this fact. */
        Debug.Assert( WO_EQ == SQLITE_INDEX_CONSTRAINT_EQ );
        Debug.Assert( WO_LT == SQLITE_INDEX_CONSTRAINT_LT );
        Debug.Assert( WO_LE == SQLITE_INDEX_CONSTRAINT_LE );
        Debug.Assert( WO_GT == SQLITE_INDEX_CONSTRAINT_GT );
        Debug.Assert( WO_GE == SQLITE_INDEX_CONSTRAINT_GE );
        Debug.Assert( WO_MATCH == SQLITE_INDEX_CONSTRAINT_MATCH );
        Debug.Assert( ( pTerm.eOperator & ( WO_EQ | WO_LT | WO_LE | WO_GT | WO_GE | WO_MATCH ) ) != 0 );
        j++;
      }
      for ( i = 0; i < nOrderBy; i++ )
      {
        Expr pExpr = pOrderBy.a[i].pExpr;
        if ( pIdxOrderBy[i] == null )
          pIdxOrderBy[i] = new sqlite3_index_orderby();
        pIdxOrderBy[i].iColumn = pExpr.iColumn;
        pIdxOrderBy[i].desc = pOrderBy.a[i].sortOrder != 0;
      }

      return pIdxInfo;
    }

    /*
    ** The table object reference passed as the second argument to this function
    ** must represent a virtual table. This function invokes the xBestIndex()
    ** method of the virtual table with the sqlite3_index_info pointer passed
    ** as the argument.
    **
    ** If an error occurs, pParse is populated with an error message and a
    ** non-zero value is returned. Otherwise, 0 is returned and the output
    ** part of the sqlite3_index_info structure is left populated.
    **
    ** Whether or not an error is returned, it is the responsibility of the
    ** caller to eventually free p.idxStr if p.needToFreeIdxStr indicates
    ** that this is required.
    */
    static int vtabBestIndex( Parse pParse, Table pTab, sqlite3_index_info p )
    {
      sqlite3_vtab pVtab = sqlite3GetVTable( pParse.db, pTab ).pVtab;
      int i;
      int rc;

#if  (SQLITE_TEST) && (SQLITE_DEBUG)
      WHERETRACE( "xBestIndex for %s\n", pTab.zName );
#endif
      TRACE_IDX_INPUTS( p );
      rc = pVtab.pModule.xBestIndex( pVtab, ref p );
      TRACE_IDX_OUTPUTS( p );

      if ( rc != SQLITE_OK )
      {
        //if ( rc == SQLITE_NOMEM )
        //{
        //  pParse.db.mallocFailed = 1;
        //}
        // else 
        if ( string.IsNullOrEmpty( pVtab.zErrMsg ) )
        {
          sqlite3ErrorMsg( pParse, "%s", sqlite3ErrStr( rc ) );
        }
        else
        {
          sqlite3ErrorMsg( pParse, "%s", pVtab.zErrMsg );
        }
      }
      //sqlite3_free( pVtab.zErrMsg );
      pVtab.zErrMsg = null;

      for ( i = 0; i < p.nConstraint; i++ )
      {
        if ( !p.aConstraint[i].usable && p.aConstraintUsage[i].argvIndex > 0 )
        {
          sqlite3ErrorMsg( pParse,
          "table %s: xBestIndex returned an invalid plan", pTab.zName );
        }
      }

      return pParse.nErr;
    }


    /*
    ** Compute the best index for a virtual table.
    **
    ** The best index is computed by the xBestIndex method of the virtual
    ** table module.  This routine is really just a wrapper that sets up
    ** the sqlite3_index_info structure that is used to communicate with
    ** xBestIndex.
    **
    ** In a join, this routine might be called multiple times for the
    ** same virtual table.  The sqlite3_index_info structure is created
    ** and initialized on the first invocation and reused on all subsequent
    ** invocations.  The sqlite3_index_info structure is also used when
    ** code is generated to access the virtual table.  The whereInfoDelete()
    ** routine takes care of freeing the sqlite3_index_info structure after
    ** everybody has finished with it.
    */
    static void bestVirtualIndex(
    Parse pParse,                  /* The parsing context */
    WhereClause pWC,               /* The WHERE clause */
    SrcList_item pSrc,             /* The FROM clause term to search */
    Bitmask notReady,              /* Mask of cursors not available for index */
    Bitmask notValid,              /* Cursors not valid for any purpose */
    ExprList pOrderBy,             /* The order by clause */
    ref WhereCost pCost,           /* Lowest cost query plan */
    ref sqlite3_index_info ppIdxInfo /* Index information passed to xBestIndex */
    )
    {
      Table pTab = pSrc.pTab;
      sqlite3_index_info pIdxInfo;
      sqlite3_index_constraint pIdxCons;
      sqlite3_index_constraint_usage[] pUsage = null;
      WhereTerm pTerm;
      int i, j;
      int nOrderBy;
      double rCost;


      /* Make sure wsFlags is initialized to some sane value. Otherwise, if the
      ** malloc in allocateIndexInfo() fails and this function returns leaving
      ** wsFlags in an uninitialized state, the caller may behave unpredictably.
      */
      pCost = new WhereCost();//memset(pCost, 0, sizeof(*pCost));
      pCost.plan.wsFlags = WHERE_VIRTUALTABLE;

      /* If the sqlite3_index_info structure has not been previously
      ** allocated and initialized, then allocate and initialize it now.
      */
      pIdxInfo = ppIdxInfo;
      if ( pIdxInfo == null )
      {
        ppIdxInfo = pIdxInfo = allocateIndexInfo( pParse, pWC, pSrc, pOrderBy );
      }
      if ( pIdxInfo == null )
      {
        return;
      }

      /* At this point, the sqlite3_index_info structure that pIdxInfo points
      ** to will have been initialized, either during the current invocation or
      ** during some prior invocation.  Now we just have to customize the
      ** details of pIdxInfo for the current invocation and pDebug.Ass it to
      ** xBestIndex.
      */

      /* The module name must be defined. Also, by this point there must
      ** be a pointer to an sqlite3_vtab structure. Otherwise
      ** sqlite3ViewGetColumnNames() would have picked up the error.
      */
      Debug.Assert( pTab.azModuleArg != null && pTab.azModuleArg[0] != null );
      Debug.Assert( sqlite3GetVTable( pParse.db, pTab ) != null );

      /* Set the aConstraint[].usable fields and initialize all
      ** output variables to zero.
      **
      ** aConstraint[].usable is true for constraints where the right-hand
      ** side contains only references to tables to the left of the current
      ** table.  In other words, if the constraint is of the form:
      **
      **           column = expr
      **
      ** and we are evaluating a join, then the constraint on column is
      ** only valid if all tables referenced in expr occur to the left
      ** of the table containing column.
      **
      ** The aConstraints[] array contains entries for all constraints
      ** on the current table.  That way we only have to compute it once
      ** even though we might try to pick the best index multiple times.
      ** For each attempt at picking an index, the order of tables in the
      ** join might be different so we have to recompute the usable flag
      ** each time.
      */
      //pIdxCons = *(struct sqlite3_index_constraint**)&pIdxInfo->aConstraint;
      //pUsage = pIdxInfo->aConstraintUsage;
      for ( i = 0; i < pIdxInfo.nConstraint; i++)
      {
        pIdxCons = pIdxInfo.aConstraint[i];
        pUsage = pIdxInfo.aConstraintUsage;
        j = pIdxCons.iTermOffset;
        pTerm = pWC.a[j];
        pIdxCons.usable = ( pTerm.prereqRight & notReady ) == 0;
        pUsage[i] = new sqlite3_index_constraint_usage();
      }
      // memset(pUsage, 0, sizeof(pUsage[0])*pIdxInfo.nConstraint);
      if ( pIdxInfo.needToFreeIdxStr!=0 )
      {
        //sqlite3_free(ref pIdxInfo.idxStr);
      }
      pIdxInfo.idxStr = null;
      pIdxInfo.idxNum = 0;
      pIdxInfo.needToFreeIdxStr = 0;
      pIdxInfo.orderByConsumed = false;
      /* ((double)2) In case of SQLITE_OMIT_FLOATING_POINT... */
      pIdxInfo.estimatedCost = SQLITE_BIG_DBL / ( (double)2 );
      nOrderBy = pIdxInfo.nOrderBy;
      if ( null == pOrderBy )
      {
        pIdxInfo.nOrderBy = 0;
      }

      if ( vtabBestIndex( pParse, pTab, pIdxInfo ) != 0 )
      {
        return;
      }

      //pIdxCons = (sqlite3_index_constraint)pIdxInfo.aConstraint;
      for ( i = 0; i < pIdxInfo.nConstraint; i++ )
      {
        if ( pUsage[i].argvIndex > 0 )
        {
          //pCost.used |= pWC.a[pIdxCons[i].iTermOffset].prereqRight;
          pCost.used |= pWC.a[pIdxInfo.aConstraint[i].iTermOffset].prereqRight;          
        }
      }

      /* If there is an ORDER BY clause, and the selected virtual table index
      ** does not satisfy it, increase the cost of the scan accordingly. This
      ** matches the processing for non-virtual tables in bestBtreeIndex().
      */
      rCost = pIdxInfo.estimatedCost;
      if ( pOrderBy != null && !pIdxInfo.orderByConsumed )
      {
        rCost += estLog( rCost ) * rCost;
      }

      /* The cost is not allowed to be larger than SQLITE_BIG_DBL (the
      ** inital value of lowestCost in this loop. If it is, then the
      ** (cost<lowestCost) test below will never be true.
      **
      ** Use "(double)2" instead of "2.0" in case OMIT_FLOATING_POINT
      ** is defined.
      */
      if ( ( SQLITE_BIG_DBL / ( (double)2 ) ) < rCost )
      {
        pCost.rCost = ( SQLITE_BIG_DBL / ( (double)2 ) );
      }
      else
      {
        pCost.rCost = rCost;
      }
      pCost.plan.u.pVtabIdx = pIdxInfo;
      if ( pIdxInfo.orderByConsumed )
      {
        pCost.plan.wsFlags |= WHERE_ORDERBY;
      }
      pCost.plan.nEq = 0;
      pIdxInfo.nOrderBy = nOrderBy;

      /* Try to find a more efficient access pattern by using multiple indexes
      ** to optimize an OR expression within the WHERE clause.
      */
      bestOrClauseIndex( pParse, pWC, pSrc, notReady, notValid, pOrderBy, pCost );
    }
#endif //* SQLITE_OMIT_VIRTUALTABLE */

    /*
** Argument pIdx is a pointer to an index structure that has an array of
** SQLITE_INDEX_SAMPLES evenly spaced samples of the first indexed column
** stored in Index.aSample. These samples divide the domain of values stored
** the index into (SQLITE_INDEX_SAMPLES+1) regions.
** Region 0 contains all values less than the first sample value. Region
** 1 contains values between the first and second samples.  Region 2 contains
** values between samples 2 and 3.  And so on.  Region SQLITE_INDEX_SAMPLES
** contains values larger than the last sample.
**
** If the index contains many duplicates of a single value, then it is
** possible that two or more adjacent samples can hold the same value.
** When that is the case, the smallest possible region code is returned
** when roundUp is false and the largest possible region code is returned
** when roundUp is true.
**
** If successful, this function determines which of the regions value 
** pVal lies in, sets *piRegion to the region index (a value between 0
** and SQLITE_INDEX_SAMPLES+1, inclusive) and returns SQLITE_OK.
** Or, if an OOM occurs while converting text values between encodings,
** SQLITE_NOMEM is returned and *piRegion is undefined.
*/
#if SQLITE_ENABLE_STAT2
    static int whereRangeRegion(
    Parse pParse,               /* Database connection */
    Index pIdx,                 /* Index to consider domain of */
    sqlite3_value pVal,         /* Value to consider */
    int roundUp,                /* Return largest valid region if true */
    out int piRegion            /* OUT: Region of domain in which value lies */
    )
    {
      piRegion = 0;
      Debug.Assert( roundUp == 0 || roundUp == 1 );
      if ( ALWAYS( pVal ) )
      {
        IndexSample[] aSample = pIdx.aSample;
        int i = 0;
        int eType = sqlite3_value_type( pVal );

        if ( eType == SQLITE_INTEGER || eType == SQLITE_FLOAT )
        {
          double r = sqlite3_value_double( pVal );
          for ( i = 0; i < SQLITE_INDEX_SAMPLES; i++ )
          {
            if ( aSample[i].eType == SQLITE_NULL )
              continue;
            if ( aSample[i].eType >= SQLITE_TEXT )
              break;
            if ( roundUp != 0 )
            {
              if ( aSample[i].u.r > r )
                break;
            }
            else
            {
              if ( aSample[i].u.r >= r )
                break;
            }
          }
        }
        else if ( eType == SQLITE_NULL )
        {
          i = 0;
          if ( roundUp != 0 )
          {
            while ( i < SQLITE_INDEX_SAMPLES && aSample[i].eType == SQLITE_NULL )
              i++;
          }
        }
        else
        {
          sqlite3 db = pParse.db;
          CollSeq pColl;
          string z;
          int n;

          /* pVal comes from sqlite3ValueFromExpr() so the type cannot be NULL */
          Debug.Assert( eType == SQLITE_TEXT || eType == SQLITE_BLOB );

          if ( eType == SQLITE_BLOB )
          {
            byte[] blob = sqlite3_value_blob( pVal );
            z = Encoding.UTF8.GetString( blob, 0, blob.Length );
            pColl = db.pDfltColl;
            Debug.Assert( pColl.enc == SQLITE_UTF8 );
          }
          else
          {
            pColl = sqlite3GetCollSeq( db, SQLITE_UTF8, null, pIdx.azColl[0] );
            if ( pColl == null )
            {
              sqlite3ErrorMsg( pParse, "no such collation sequence: %s",
                  pIdx.azColl );
              return SQLITE_ERROR;
            }
            z = sqlite3ValueText( pVal, pColl.enc );
            //if( null==z ){
            //  return SQLITE_NOMEM;
            //}
            Debug.Assert( z != string.Empty && pColl != null && pColl.xCmp != null );
          }
          n = sqlite3ValueBytes( pVal, pColl.enc );

          for ( i = 0; i < SQLITE_INDEX_SAMPLES; i++ )
          {
            int c;
            int eSampletype = aSample[i].eType;
            if ( eSampletype == SQLITE_NULL || eSampletype < eType )
              continue;
            if ( ( eSampletype != eType ) )
              break;
#if !SQLITE_OMIT_UTF16
if( pColl.enc!=SQLITE_UTF8 ){
int nSample;
string zSample;
zSample = sqlite3Utf8to16(
db, pColl.enc, aSample[i].u.z, aSample[i].nByte, ref nSample
);
zSample = aSample[i].u.z;
nSample = aSample[i].u.z.Length;
//if( null==zSample ){
//  Debug.Assert( db.mallocFailed );
//  return SQLITE_NOMEM;
//}
c = pColl.xCmp(pColl.pUser, nSample, zSample, n, z);
sqlite3DbFree(db, ref zSample);
}else
#endif
            {
              c = pColl.xCmp( pColl.pUser, aSample[i].nByte, aSample[i].u.z, n, z );
            }
            if ( c - roundUp >= 0 )
              break;
          }
        }

        Debug.Assert( i >= 0 && i <= SQLITE_INDEX_SAMPLES );
        piRegion = i;
      }
      return SQLITE_OK;
    }
#endif   //* #if SQLITE_ENABLE_STAT2 */

    /*
** If expression pExpr represents a literal value, set *pp to point to
** an sqlite3_value structure containing the same value, with affinity
** aff applied to it, before returning. It is the responsibility of the 
** caller to eventually release this structure by passing it to 
** sqlite3ValueFree().
**
** If the current parse is a recompile (sqlite3Reprepare()) and pExpr
** is an SQL variable that currently has a non-NULL value bound to it,
** create an sqlite3_value structure containing this value, again with
** affinity aff applied to it, instead.
**
** If neither of the above apply, set *pp to NULL.
**
** If an error occurs, return an error code. Otherwise, SQLITE_OK.
*/
#if SQLITE_ENABLE_STAT2
    static int valueFromExpr(
    Parse pParse,
    Expr pExpr,
    char aff,
    ref sqlite3_value pp
    )
    {
      if ( pExpr.op == TK_VARIABLE
      || ( pExpr.op == TK_REGISTER && pExpr.op2 == TK_VARIABLE )
      )
      {
        int iVar = pExpr.iColumn;
        sqlite3VdbeSetVarmask( pParse.pVdbe, iVar ); /* IMP: R-23257-02778 */
        pp = sqlite3VdbeGetValue( pParse.pReprepare, iVar, (u8)aff );
        return SQLITE_OK;
      }
      return sqlite3ValueFromExpr( pParse.db, pExpr, SQLITE_UTF8, aff, ref pp );
    }
#endif

    /*
** This function is used to estimate the number of rows that will be visited
** by scanning an index for a range of values. The range may have an upper
** bound, a lower bound, or both. The WHERE clause terms that set the upper
** and lower bounds are represented by pLower and pUpper respectively. For
** example, assuming that index p is on t1(a):
**
**   ... FROM t1 WHERE a > ? AND a < ? ...
**                    |_____|   |_____|
**                       |         |
**                     pLower    pUpper
**
** If either of the upper or lower bound is not present, then NULL is passed in
** place of the corresponding WhereTerm.
**
** The nEq parameter is passed the index of the index column subject to the
** range constraint. Or, equivalently, the number of equality constraints
** optimized by the proposed index scan. For example, assuming index p is
** on t1(a, b), and the SQL query is:
**
**   ... FROM t1 WHERE a = ? AND b > ? AND b < ? ...
**
** then nEq should be passed the value 1 (as the range restricted column,
** b, is the second left-most column of the index). Or, if the query is:
**
**   ... FROM t1 WHERE a > ? AND a < ? ...
**
** then nEq should be passed 0.
**
** The returned value is an integer between 1 and 100, inclusive. A return
** value of 1 indicates that the proposed range scan is expected to visit
** approximately 1/100th (1%) of the rows selected by the nEq equality
** constraints (if any). A return value of 100 indicates that it is expected
** that the range scan will visit every row (100%) selected by the equality
** constraints.
**
** In the absence of sqlite_stat2 ANALYZE data, each range inequality
** reduces the search space by 3/4ths.  Hence a single constraint (x>?)
** results in a return of 25 and a range constraint (x>? AND x<?) results
** in a return of 6.
*/
    static int whereRangeScanEst(
    Parse pParse,       /* Parsing & code generating context */
    Index p,            /* The index containing the range-compared column; "x" */
    int nEq,            /* index into p.aCol[] of the range-compared column */
    WhereTerm pLower,   /* Lower bound on the range. ex: "x>123" Might be NULL */
    WhereTerm pUpper,   /* Upper bound on the range. ex: "x<455" Might be NULL */
    out int piEst       /* OUT: Return value */
    )
    {
      int rc = SQLITE_OK;

#if SQLITE_ENABLE_STAT2

      if ( nEq == 0 && p.aSample != null )
      {
        sqlite3_value pLowerVal = null;
        sqlite3_value pUpperVal = null;
        int iEst;
        int iLower = 0;
        int iUpper = SQLITE_INDEX_SAMPLES;
        int roundUpUpper = 0;
        int roundUpLower = 0;
        char aff = p.pTable.aCol[p.aiColumn[0]].affinity;

        if ( pLower != null )
        {
          Expr pExpr = pLower.pExpr.pRight;
          rc = valueFromExpr( pParse, pExpr, aff, ref pLowerVal );
          Debug.Assert( pLower.eOperator == WO_GT || pLower.eOperator == WO_GE );
          roundUpLower = ( pLower.eOperator == WO_GT ) ? 1 : 0;
        }
        if ( rc == SQLITE_OK && pUpper != null )
        {
          Expr pExpr = pUpper.pExpr.pRight;
          rc = valueFromExpr( pParse, pExpr, aff, ref pUpperVal );
          Debug.Assert( pUpper.eOperator == WO_LT || pUpper.eOperator == WO_LE );
          roundUpUpper = ( pUpper.eOperator == WO_LE ) ? 1 : 0;
        }

        if ( rc != SQLITE_OK || ( pLowerVal == null && pUpperVal == null ) )
        {
          sqlite3ValueFree( ref pLowerVal );
          sqlite3ValueFree( ref pUpperVal );
          goto range_est_fallback;
        }
        else if ( pLowerVal == null )
        {
          rc = whereRangeRegion( pParse, p, pUpperVal, roundUpUpper, out iUpper );
          if ( pLower != null )
            iLower = iUpper / 2;
        }
        else if ( pUpperVal == null )
        {
          rc = whereRangeRegion( pParse, p, pLowerVal, roundUpLower, out iLower );
          if ( pUpper != null )
            iUpper = ( iLower + SQLITE_INDEX_SAMPLES + 1 ) / 2;
        }
        else
        {
          rc = whereRangeRegion( pParse, p, pUpperVal, roundUpUpper, out iUpper );
          if ( rc == SQLITE_OK )
          {
            rc = whereRangeRegion( pParse, p, pLowerVal, roundUpLower, out iLower );
          }
        }
        WHERETRACE( "range scan regions: %d..%d\n", iLower, iUpper );

        iEst = iUpper - iLower;
        testcase( iEst == SQLITE_INDEX_SAMPLES );
        Debug.Assert( iEst <= SQLITE_INDEX_SAMPLES );
        if ( iEst < 1 )
        {
          piEst = 50 / SQLITE_INDEX_SAMPLES;
        }
        else
        {
          piEst = ( iEst * 100 ) / SQLITE_INDEX_SAMPLES;
        }

        sqlite3ValueFree( ref pLowerVal );
        sqlite3ValueFree( ref pUpperVal );
        return rc;
      }
range_est_fallback:
#else
UNUSED_PARAMETER(pParse);
UNUSED_PARAMETER(p);
UNUSED_PARAMETER(nEq);
#endif
      Debug.Assert( pLower != null || pUpper != null );
      piEst = 100;
      if ( pLower != null && ( pLower.wtFlags & TERM_VNULL ) == 0 )
        piEst /= 4;
      if ( pUpper != null )
        piEst /= 4;
      return rc;
    }

#if SQLITE_ENABLE_STAT2
    /*
** Estimate the number of rows that will be returned based on
** an equality constraint x=VALUE and where that VALUE occurs in
** the histogram data.  This only works when x is the left-most
** column of an index and sqlite_stat2 histogram data is available
** for that index.  When pExpr==NULL that means the constraint is
** "x IS NULL" instead of "x=VALUE".
**
** Write the estimated row count into *pnRow and return SQLITE_OK. 
** If unable to make an estimate, leave *pnRow unchanged and return
** non-zero.
**
** This routine can fail if it is unable to load a collating sequence
** required for string comparison, or if unable to allocate memory
** for a UTF conversion required for comparison.  The error is stored
** in the pParse structure.
*/
    static int whereEqualScanEst(
      Parse pParse,       /* Parsing & code generating context */
      Index p,            /* The index whose left-most column is pTerm */
      Expr pExpr,         /* Expression for VALUE in the x=VALUE constraint */
      ref double pnRow    /* Write the revised row estimate here */
    )
    {
      sqlite3_value pRhs = null;/* VALUE on right-hand side of pTerm */
      int iLower = 0;
      int iUpper = 0;           /* Range of histogram regions containing pRhs */
      char aff;                 /* Column affinity */
      int rc;                   /* Subfunction return code */
      double nRowEst;           /* New estimate of the number of rows */

      Debug.Assert( p.aSample != null );
      aff = p.pTable.aCol[p.aiColumn[0]].affinity;
      if ( pExpr != null )
      {
        rc = valueFromExpr( pParse, pExpr, aff, ref pRhs );
        if ( rc != 0 )
          goto whereEqualScanEst_cancel;
      }
      else
      {
        pRhs = sqlite3ValueNew( pParse.db );
      }
      if ( pRhs == null )
        return SQLITE_NOTFOUND;
      rc = whereRangeRegion( pParse, p, pRhs, 0, out iLower );
      if ( rc != 0 )
        goto whereEqualScanEst_cancel;
      rc = whereRangeRegion( pParse, p, pRhs, 1, out iUpper );
      if ( rc != 0 )
        goto whereEqualScanEst_cancel;
      WHERETRACE( "equality scan regions: %d..%d\n", iLower, iUpper );
      if ( iLower >= iUpper )
      {
        nRowEst = p.aiRowEst[0] / ( SQLITE_INDEX_SAMPLES * 2 );
        if ( nRowEst < pnRow )
          pnRow = nRowEst;
      }
      else
      {
        nRowEst = ( iUpper - iLower ) * p.aiRowEst[0] / SQLITE_INDEX_SAMPLES;
        pnRow = nRowEst;
      }

whereEqualScanEst_cancel:
      sqlite3ValueFree( ref pRhs );
      return rc;
    }
#endif //* defined(SQLITE_ENABLE_STAT2) */

#if SQLITE_ENABLE_STAT2
    /*
** Estimate the number of rows that will be returned based on
** an IN constraint where the right-hand side of the IN operator
** is a list of values.  Example:
**
**        WHERE x IN (1,2,3,4)
**
** Write the estimated row count into *pnRow and return SQLITE_OK. 
** If unable to make an estimate, leave *pnRow unchanged and return
** non-zero.
**
** This routine can fail if it is unable to load a collating sequence
** required for string comparison, or if unable to allocate memory
** for a UTF conversion required for comparison.  The error is stored
** in the pParse structure.
*/
    static int whereInScanEst(
      Parse pParse,       /* Parsing & code generating context */
      Index p,            /* The index whose left-most column is pTerm */
      ExprList pList,     /* The value list on the RHS of "x IN (v1,v2,v3,...)" */
      ref double pnRow    /* Write the revised row estimate here */
    )
    {
      sqlite3_value pVal = null;/* One value from list */
      int iLower = 0;
      int iUpper = 0;           /* Range of histogram regions containing pRhs */
      char aff;                 /* Column affinity */
      int rc = SQLITE_OK;       /* Subfunction return code */
      double nRowEst;           /* New estimate of the number of rows */
      int nSpan = 0;            /* Number of histogram regions spanned */
      int nSingle = 0;          /* Histogram regions hit by a single value */
      int nNotFound = 0;        /* Count of values that are not constants */
      int i;                               /* Loop counter */
      u8[] aSpan = new u8[SQLITE_INDEX_SAMPLES + 1];    /* Histogram regions that are spanned */
      u8[] aSingle = new u8[SQLITE_INDEX_SAMPLES + 1];  /* Histogram regions hit once */

      Debug.Assert( p.aSample != null );
      aff = p.pTable.aCol[p.aiColumn[0]].affinity;
      //memset(aSpan, 0, sizeof(aSpan));
      //memset(aSingle, 0, sizeof(aSingle));
      for ( i = 0; i < pList.nExpr; i++ )
      {
        sqlite3ValueFree( ref pVal );
        rc = valueFromExpr( pParse, pList.a[i].pExpr, aff, ref pVal );
        if ( rc != 0 )
          break;
        if ( pVal == null || sqlite3_value_type( pVal ) == SQLITE_NULL )
        {
          nNotFound++;
          continue;
        }
        rc = whereRangeRegion( pParse, p, pVal, 0, out iLower );
        if ( rc != 0 )
          break;
        rc = whereRangeRegion( pParse, p, pVal, 1, out iUpper );
        if ( rc != 0 )
          break;
        if ( iLower >= iUpper )
        {
          aSingle[iLower] = 1;
        }
        else
        {
          Debug.Assert( iLower >= 0 && iUpper <= SQLITE_INDEX_SAMPLES );
          while ( iLower < iUpper )
            aSpan[iLower++] = 1;
        }
      }
      if ( rc == SQLITE_OK )
      {
        for ( i = nSpan = 0; i <= SQLITE_INDEX_SAMPLES; i++ )
        {
          if ( aSpan[i] != 0 )
          {
            nSpan++;
          }
          else if ( aSingle[i] != 0 )
          {
            nSingle++;
          }
        }
        nRowEst = ( nSpan * 2 + nSingle ) * p.aiRowEst[0] / ( 2 * SQLITE_INDEX_SAMPLES )
                   + nNotFound * p.aiRowEst[1];
        if ( nRowEst > p.aiRowEst[0] )
          nRowEst = p.aiRowEst[0];
        pnRow = nRowEst;
        WHERETRACE( "IN row estimate: nSpan=%d, nSingle=%d, nNotFound=%d, est=%g\n",
                     nSpan, nSingle, nNotFound, nRowEst );
      }
      sqlite3ValueFree( ref pVal );
      return rc;
    }
#endif //* defined(SQLITE_ENABLE_STAT2) */


    /*
** Find the best query plan for accessing a particular table.  Write the
** best query plan and its cost into the WhereCost object supplied as the
** last parameter.
**
** The lowest cost plan wins.  The cost is an estimate of the amount of
** CPU and disk I/O needed to process the requested result.
** Factors that influence cost include:
**
**    *  The estimated number of rows that will be retrieved.  (The
**       fewer the better.)
**
**    *  Whether or not sorting must occur.
**
**    *  Whether or not there must be separate lookups in the
**       index and in the main table.
**
** If there was an INDEXED BY clause (pSrc->pIndex) attached to the table in
** the SQL statement, then this function only considers plans using the 
** named index. If no such plan is found, then the returned cost is
** SQLITE_BIG_DBL. If a plan is found that uses the named index, 
** then the cost is calculated in the usual way.
**
** If a NOT INDEXED clause (pSrc->notIndexed!=0) was attached to the table 
** in the SELECT statement, then no indexes are considered. However, the 
** selected plan may still take advantage of the built-in rowid primary key
** index.
*/
    static void bestBtreeIndex(
    Parse pParse,              /* The parsing context */
    WhereClause pWC,           /* The WHERE clause */
    SrcList_item pSrc,         /* The FROM clause term to search */
    Bitmask notReady,          /* Mask of cursors not available for indexing */
    Bitmask notValid,          /* Cursors not available for any purpose */
    ExprList pOrderBy,         /* The ORDER BY clause */
    ref WhereCost pCost        /* Lowest cost query plan */
    )
    {
      int iCur = pSrc.iCursor;    /* The cursor of the table to be accessed */
      Index pProbe;               /* An index we are evaluating */
      Index pIdx;                 /* Copy of pProbe, or zero for IPK index */
      u32 eqTermMask;             /* Current mask of valid equality operators */
      u32 idxEqTermMask;          /* Index mask of valid equality operators */
      Index sPk;                  /* A fake index object for the primary key */
      int[] aiRowEstPk = new int[2]; /* The aiRowEst[] value for the sPk index */
      int aiColumnPk = -1;        /* The aColumn[] value for the sPk index */
      int wsFlagMask;             /* Allowed flags in pCost.plan.wsFlag */

      /* Initialize the cost to a worst-case value */
      if ( pCost == null )
        pCost = new WhereCost();
      else
        pCost.Clear();  //memset(pCost, 0, sizeof(*pCost));
      pCost.rCost = SQLITE_BIG_DBL;

      /* If the pSrc table is the right table of a LEFT JOIN then we may not
      ** use an index to satisfy IS NULL constraints on that table.  This is
      ** because columns might end up being NULL if the table does not match -
      ** a circumstance which the index cannot help us discover.  Ticket #2177.
      */
      if ( ( pSrc.jointype & JT_LEFT ) != 0 )
      {
        idxEqTermMask = WO_EQ | WO_IN;
      }
      else
      {
        idxEqTermMask = WO_EQ | WO_IN | WO_ISNULL;
      }

      if ( pSrc.pIndex != null )
      {
        /* An INDEXED BY clause specifies a particular index to use */
        pIdx = pProbe = pSrc.pIndex;
        wsFlagMask = ~( WHERE_ROWID_EQ | WHERE_ROWID_RANGE );
        eqTermMask = idxEqTermMask;
      }
      else
      {
        /* There is no INDEXED BY clause.  Create a fake Index object in local
        ** variable sPk to represent the rowid primary key index.  Make this
        ** fake index the first in a chain of Index objects with all of the real
        ** indices to follow */
        Index pFirst;                  /* First of real indices on the table */
        sPk = new Index(); // memset( &sPk, 0, sizeof( Index ) );
        sPk.aSortOrder = new byte[1];
        sPk.azColl = new string[1];
        sPk.azColl[0] = string.Empty;
        sPk.nColumn = 1;
        sPk.aiColumn = new int[1];
        sPk.aiColumn[0] = aiColumnPk;
        sPk.aiRowEst = aiRowEstPk;
        sPk.onError = OE_Replace;
        sPk.pTable = pSrc.pTab;
        aiRowEstPk[0] = (int)pSrc.pTab.nRowEst;
        aiRowEstPk[1] = 1;
        pFirst = pSrc.pTab.pIndex;
        if ( pSrc.notIndexed == 0 )
        {
          /* The real indices of the table are only considered if the
          ** NOT INDEXED qualifier is omitted from the FROM clause */
          sPk.pNext = pFirst;
        }
        pProbe = sPk;
        wsFlagMask = ~(
        WHERE_COLUMN_IN | WHERE_COLUMN_EQ | WHERE_COLUMN_NULL | WHERE_COLUMN_RANGE
        );
        eqTermMask = WO_EQ | WO_IN;
        pIdx = null;
      }

      /* Loop over all indices looking for the best one to use
      */
      for ( ; pProbe != null; pIdx = pProbe = pProbe.pNext )
      {
        int[] aiRowEst = pProbe.aiRowEst;
        double cost;                /* Cost of using pProbe */
        double nRow;                /* Estimated number of rows in result set */
        double log10N = 0;          /* base-10 logarithm of nRow (inexact) */
        int rev = 0;                /* True to scan in reverse order */
        int wsFlags = 0;
        Bitmask used = 0;

        /* The following variables are populated based on the properties of
        ** index being evaluated. They are then used to determine the expected
        ** cost and number of rows returned.
        **
        **  nEq: 
        **    Number of equality terms that can be implemented using the index.
        **    In other words, the number of initial fields in the index that
        **    are used in == or IN or NOT NULL constraints of the WHERE clause.
        **
        **  nInMul:  
        **    The "in-multiplier". This is an estimate of how many seek operations 
        **    SQLite must perform on the index in question. For example, if the 
        **    WHERE clause is:
        **
        **      WHERE a IN (1, 2, 3) AND b IN (4, 5, 6)
        **
        **    SQLite must perform 9 lookups on an index on (a, b), so nInMul is 
        **    set to 9. Given the same schema and either of the following WHERE 
        **    clauses:
        **
        **      WHERE a =  1
        **      WHERE a >= 2
        **
        **    nInMul is set to 1.
        **
        **    If there exists a WHERE term of the form "x IN (SELECT ...)", then 
        **    the sub-select is assumed to return 25 rows for the purposes of 
        **    determining nInMul.
        **
        **  bInEst:  
        **    Set to true if there was at least one "x IN (SELECT ...)" term used 
        **    in determining the value of nInMul.  Note that the RHS of the
        **    IN operator must be a SELECT, not a value list, for this variable
        **    to be true.
        **
        **  estBound:
        **    An estimate on the amount of the table that must be searched.  A
        **    value of 100 means the entire table is searched.  Range constraints
        **    might reduce this to a value less than 100 to indicate that only
        **    a fraction of the table needs searching.  In the absence of
        **    sqlite_stat2 ANALYZE data, a single inequality reduces the search
        **    space to 1/4rd its original size.  So an x>? constraint reduces
        **    estBound to 25.  Two constraints (x>? AND x<?) reduce estBound to 6.
        **
        **  bSort:   
        **    Boolean. True if there is an ORDER BY clause that will require an 
        **    external sort (i.e. scanning the index being evaluated will not 
        **    correctly order records).
        **
        **  bLookup: 
        **    Boolean. True if a table lookup is required for each index entry
        **    visited.  In other words, true if this is not a covering index.
        **    This is always false for the rowid primary key index of a table.
        **    For other indexes, it is true unless all the columns of the table
        **    used by the SELECT statement are present in the index (such an
        **    index is sometimes described as a covering index).
        **    For example, given the index on (a, b), the second of the following 
        **    two queries requires table b-tree lookups in order to find the value
        **    of column c, but the first does not because columns a and b are
        **    both available in the index.
        **
        **             SELECT a, b    FROM tbl WHERE a = 1;
        **             SELECT a, b, c FROM tbl WHERE a = 1;
        */
        int nEq;                      /* Number of == or IN terms matching index */
        int bInEst = 0;               /* True if "x IN (SELECT...)" seen */
        int nInMul = 1;               /* Number of distinct equalities to lookup */
        int estBound = 100;           /* Estimated reduction in search space */
        int nBound = 0;               /* Number of range constraints seen */
        int bSort = 0;                /* True if external sort required */
        int bLookup = 0;              /* True if not a covering index */
        WhereTerm pTerm;              /* A single term of the WHERE clause */
#if SQLITE_ENABLE_STAT2
        WhereTerm pFirstTerm = null;  /* First term matching the index */
#endif

        /* Determine the values of nEq and nInMul */
        for ( nEq = 0; nEq < pProbe.nColumn; nEq++ )
        {
          int j = pProbe.aiColumn[nEq];
          pTerm = findTerm( pWC, iCur, j, notReady, eqTermMask, pIdx );
          if ( pTerm == null )
            break;
          wsFlags |= ( WHERE_COLUMN_EQ | WHERE_ROWID_EQ );
          if ( ( pTerm.eOperator & WO_IN ) != 0 )
          {
            Expr pExpr = pTerm.pExpr;
            wsFlags |= WHERE_COLUMN_IN;
            if ( ExprHasProperty( pExpr, EP_xIsSelect ) )
            {
              /* "x IN (SELECT ...)":  Assume the SELECT returns 25 rows */
              nInMul *= 25;
              bInEst = 1;
            }
            else if ( ALWAYS( pExpr.x.pList != null ) && pExpr.x.pList.nExpr != 0 )
            {
              /* "x IN (value, value, ...)" */
              nInMul *= pExpr.x.pList.nExpr;
            }
          }
          else if ( ( pTerm.eOperator & WO_ISNULL ) != 0 )
          {
            wsFlags |= WHERE_COLUMN_NULL;
          }
#if SQLITE_ENABLE_STAT2
          if ( nEq == 0 && pProbe.aSample != null )
            pFirstTerm = pTerm;
#endif
          used |= pTerm.prereqRight;
        }

        /* Determine the value of estBound. */
        if ( nEq < pProbe.nColumn && pProbe.bUnordered == 0 )
        {
          int j = pProbe.aiColumn[nEq];
          if ( findTerm( pWC, iCur, j, notReady, WO_LT | WO_LE | WO_GT | WO_GE, pIdx ) != null )
          {
            WhereTerm pTop = findTerm( pWC, iCur, j, notReady, WO_LT | WO_LE, pIdx );
            WhereTerm pBtm = findTerm( pWC, iCur, j, notReady, WO_GT | WO_GE, pIdx );
            whereRangeScanEst( pParse, pProbe, nEq, pBtm, pTop, out estBound );
            if ( pTop != null )
            {
              nBound = 1;
              wsFlags |= WHERE_TOP_LIMIT;
              used |= pTop.prereqRight;
            }
            if ( pBtm != null )
            {
              nBound++;
              wsFlags |= WHERE_BTM_LIMIT;
              used |= pBtm.prereqRight;
            }
            wsFlags |= ( WHERE_COLUMN_RANGE | WHERE_ROWID_RANGE );
          }
        }
        else if ( pProbe.onError != OE_None )
        {
          testcase( wsFlags & WHERE_COLUMN_IN );
          testcase( wsFlags & WHERE_COLUMN_NULL );
          if ( ( wsFlags & ( WHERE_COLUMN_IN | WHERE_COLUMN_NULL ) ) == 0 )
          {
            wsFlags |= WHERE_UNIQUE;
          }
        }

        /* If there is an ORDER BY clause and the index being considered will
        ** naturally scan rows in the required order, set the appropriate flags
        ** in wsFlags. Otherwise, if there is an ORDER BY clause but the index
        ** will scan rows in a different order, set the bSort variable.  */
        if ( pOrderBy != null )
        {
          if ( ( wsFlags & WHERE_COLUMN_IN ) == 0
            && pProbe.bUnordered == 0
            && isSortingIndex( pParse, pWC.pMaskSet, pProbe, iCur, pOrderBy,
                              nEq, wsFlags, ref rev )
          )
          {
            wsFlags |= WHERE_ROWID_RANGE | WHERE_COLUMN_RANGE | WHERE_ORDERBY;
            wsFlags |= ( rev != 0 ? WHERE_REVERSE : 0 );
          }
          else
          {
            bSort = 1;
          }
        }

        /* If currently calculating the cost of using an index (not the IPK
        ** index), determine if all required column data may be obtained without 
        ** using the main table (i.e. if the index is a covering
        ** index for this query). If it is, set the WHERE_IDX_ONLY flag in
        ** wsFlags. Otherwise, set the bLookup variable to true.  */
        if ( pIdx != null && wsFlags != 0 )
        {
          Bitmask m = pSrc.colUsed;
          int j;
          for ( j = 0; j < pIdx.nColumn; j++ )
          {
            int x = pIdx.aiColumn[j];
            if ( x < BMS - 1 )
            {
              m &= ~( ( (Bitmask)1 ) << x );
            }
          }
          if ( m == 0 )
          {
            wsFlags |= WHERE_IDX_ONLY;
          }
          else
          {
            bLookup = 1;
          }
        }

        /*
        ** Estimate the number of rows of output.  For an "x IN (SELECT...)"
        ** constraint, do not let the estimate exceed half the rows in the table.
        */
        nRow = (double)( aiRowEst[nEq] * nInMul );
        if ( bInEst != 0 && nRow * 2 > aiRowEst[0] )
        {
          nRow = aiRowEst[0] / 2;
          nInMul = (int)( nRow / aiRowEst[nEq] );
        }

#if SQLITE_ENABLE_STAT2
        /* If the constraint is of the form x=VALUE and histogram
    ** data is available for column x, then it might be possible
    ** to get a better estimate on the number of rows based on
    ** VALUE and how common that value is according to the histogram.
    */
        if ( nRow > (double)1 && nEq == 1 && pFirstTerm != null )
        {
          if ( ( pFirstTerm.eOperator & ( WO_EQ | WO_ISNULL ) ) != 0 )
          {
            testcase( pFirstTerm.eOperator == WO_EQ );
            testcase( pFirstTerm.eOperator == WO_ISNULL );
            whereEqualScanEst( pParse, pProbe, pFirstTerm.pExpr.pRight, ref nRow );
          }
          else if ( pFirstTerm.eOperator == WO_IN && bInEst == 0 )
          {
            whereInScanEst( pParse, pProbe, pFirstTerm.pExpr.x.pList, ref nRow );
          }
        }
#endif //* SQLITE_ENABLE_STAT2 */

        /* Adjust the number of output rows and downward to reflect rows
    ** that are excluded by range constraints.
    */
        nRow = ( nRow * (double)estBound ) / (double)100;
        if ( nRow < 1 )
          nRow = 1;

        /* Experiments run on real SQLite databases show that the time needed
        ** to do a binary search to locate a row in a table or index is roughly
        ** log10(N) times the time to move from one row to the next row within
        ** a table or index.  The actual times can vary, with the size of
        ** records being an important factor.  Both moves and searches are
        ** slower with larger records, presumably because fewer records fit
        ** on one page and hence more pages have to be fetched.
        **
        ** The ANALYZE command and the sqlite_stat1 and sqlite_stat2 tables do
        ** not give us data on the relative sizes of table and index records.
        ** So this computation assumes table records are about twice as big
        ** as index records
        */
        if ( ( wsFlags & WHERE_NOT_FULLSCAN ) == 0 )
        {
          /* The cost of a full table scan is a number of move operations equal
          ** to the number of rows in the table.
          **
          ** We add an additional 4x penalty to full table scans.  This causes
          ** the cost function to err on the side of choosing an index over
          ** choosing a full scan.  This 4x full-scan penalty is an arguable
          ** decision and one which we expect to revisit in the future.  But
          ** it seems to be working well enough at the moment.
          */
          cost = aiRowEst[0] * 4;
        }
        else
        {
          log10N = estLog( aiRowEst[0] );
          cost = nRow;
          if ( pIdx != null )
          {
            if ( bLookup != 0 )
            {
              /* For an index lookup followed by a table lookup:
              **    nInMul index searches to find the start of each index range
              **  + nRow steps through the index
              **  + nRow table searches to lookup the table entry using the rowid
              */
              cost += ( nInMul + nRow ) * log10N;
            }
            else
            {
              /* For a covering index:
              **     nInMul index searches to find the initial entry 
              **   + nRow steps through the index
              */
              cost += nInMul * log10N;
            }
          }
          else
          {
            /* For a rowid primary key lookup:
            **    nInMult table searches to find the initial entry for each range
            **  + nRow steps through the table
            */
            cost += nInMul * log10N;
          }
        }

        /* Add in the estimated cost of sorting the result.  Actual experimental
        ** measurements of sorting performance in SQLite show that sorting time
        ** adds C*N*log10(N) to the cost, where N is the number of rows to be 
        ** sorted and C is a factor between 1.95 and 4.3.  We will split the
        ** difference and select C of 3.0.
        */
        if ( bSort != 0 )
        {
          cost += nRow * estLog( nRow ) * 3;
        }

        /**** Cost of using this index has now been computed ****/

        /* If there are additional constraints on this table that cannot
        ** be used with the current index, but which might lower the number
        ** of output rows, adjust the nRow value accordingly.  This only 
        ** matters if the current index is the least costly, so do not bother
        ** with this step if we already know this index will not be chosen.
        ** Also, never reduce the output row count below 2 using this step.
        **
        ** It is critical that the notValid mask be used here instead of
        ** the notReady mask.  When computing an "optimal" index, the notReady
        ** mask will only have one bit set - the bit for the current table.
        ** The notValid mask, on the other hand, always has all bits set for
        ** tables that are not in outer loops.  If notReady is used here instead
        ** of notValid, then a optimal index that depends on inner joins loops
        ** might be selected even when there exists an optimal index that has
        ** no such dependency.
        */
        if ( nRow > 2 && cost <= pCost.rCost )
        {
          //int k;                       /* Loop counter */
          int nSkipEq = nEq;           /* Number of == constraints to skip */
          int nSkipRange = nBound;     /* Number of < constraints to skip */
          Bitmask thisTab;             /* Bitmap for pSrc */

          thisTab = getMask( pWC.pMaskSet, iCur );
          for ( int ipTerm = 0, k = pWC.nTerm; nRow > 2 && k != 0; k--, ipTerm++ )//pTerm++)
          {
            pTerm = pWC.a[ipTerm];
            if ( ( pTerm.wtFlags & TERM_VIRTUAL ) != 0 )
              continue;
            if ( ( pTerm.prereqAll & notValid ) != thisTab )
              continue;
            if ( ( pTerm.eOperator & ( WO_EQ | WO_IN | WO_ISNULL ) ) != 0 )
            {
              if ( nSkipEq != 0 )
              {
                /* Ignore the first nEq equality matches since the index
                ** has already accounted for these */
                nSkipEq--;
              }
              else
              {
                /* Assume each additional equality match reduces the result
                ** set size by a factor of 10 */
                nRow /= 10;
              }
            }
            else if ( ( pTerm.eOperator & ( WO_LT | WO_LE | WO_GT | WO_GE ) ) != 0 )
            {
              if ( nSkipRange != 0 )
              {
                /* Ignore the first nSkipRange range constraints since the index
                ** has already accounted for these */
                nSkipRange--;
              }
              else
              {
                /* Assume each additional range constraint reduces the result
                ** set size by a factor of 3.  Indexed range constraints reduce
                ** the search space by a larger factor: 4.  We make indexed range
                ** more selective intentionally because of the subjective 
                ** observation that indexed range constraints really are more
                ** selective in practice, on average. */
                nRow /= 3;
              }
            }
            else if ( pTerm.eOperator != WO_NOOP )
            {
              /* Any other expression lowers the output row count by half */
              nRow /= 2;
            }
          }
          if ( nRow < 2 )
            nRow = 2;
        }

#if  (SQLITE_TEST) && (SQLITE_DEBUG)
        WHERETRACE(
        "%s(%s): nEq=%d nInMul=%d estBound=%d bSort=%d bLookup=%d wsFlags=0x%x\n" +
      "         notReady=0x%llx log10N=%.1f nRow=%.1f cost=%.1f used=0x%llx\n",
        pSrc.pTab.zName, ( pIdx != null ? pIdx.zName : "ipk" ),
        nEq, nInMul, estBound, bSort, bLookup, wsFlags,
        notReady, log10N, cost, used
        );
#endif
        /* If this index is the best we have seen so far, then record this
** index and its cost in the pCost structure.
*/
        if ( ( null == pIdx || wsFlags != 0 )
        && ( cost < pCost.rCost || ( cost <= pCost.rCost && nRow < pCost.plan.nRow ) )
        )
        {
          pCost.rCost = cost;
          pCost.used = used;
          pCost.plan.nRow = nRow;
          pCost.plan.wsFlags = (uint)( wsFlags & wsFlagMask );
          pCost.plan.nEq = (uint)nEq;
          pCost.plan.u.pIdx = pIdx;
        }

        /* If there was an INDEXED BY clause, then only that one index is
        ** considered. */
        if ( pSrc.pIndex != null )
          break;

        /* Reset masks for the next index in the loop */
        wsFlagMask = ~( WHERE_ROWID_EQ | WHERE_ROWID_RANGE );
        eqTermMask = idxEqTermMask;
      }

      /* If there is no ORDER BY clause and the SQLITE_ReverseOrder flag
      ** is set, then reverse the order that the index will be scanned
      ** in. This is used for application testing, to help find cases
      ** where application behaviour depends on the (undefined) order that
      ** SQLite outputs rows in in the absence of an ORDER BY clause.  */
      if ( null == pOrderBy && ( pParse.db.flags & SQLITE_ReverseOrder ) != 0 )
      {
        pCost.plan.wsFlags |= WHERE_REVERSE;
      }

      Debug.Assert( pOrderBy != null || ( pCost.plan.wsFlags & WHERE_ORDERBY ) == 0 );
      Debug.Assert( pCost.plan.u.pIdx == null || ( pCost.plan.wsFlags & WHERE_ROWID_EQ ) == 0 );
      Debug.Assert( pSrc.pIndex == null
      || pCost.plan.u.pIdx == null
      || pCost.plan.u.pIdx == pSrc.pIndex
      );

#if  (SQLITE_TEST) && (SQLITE_DEBUG)
      WHERETRACE( "best index is: %s\n",
      ( ( pCost.plan.wsFlags & WHERE_NOT_FULLSCAN ) == 0 ? "none" :
      pCost.plan.u.pIdx != null ? pCost.plan.u.pIdx.zName : "ipk" )
      );
#endif
      bestOrClauseIndex( pParse, pWC, pSrc, notReady, notValid, pOrderBy, pCost );
      bestAutomaticIndex( pParse, pWC, pSrc, notReady, pCost );
      pCost.plan.wsFlags |= (u32)eqTermMask;
    }


    /*
    ** Find the query plan for accessing table pSrc.pTab. Write the
    ** best query plan and its cost into the WhereCost object supplied
    ** as the last parameter. This function may calculate the cost of
    ** both real and virtual table scans.
    */
    static void bestIndex(
    Parse pParse,               /* The parsing context */
    WhereClause pWC,            /* The WHERE clause */
    SrcList_item pSrc,          /* The FROM clause term to search */
    Bitmask notReady,           /* Mask of cursors not available for indexing */
    Bitmask notValid,           /* Cursors not available for any purpose */
    ExprList pOrderBy,          /* The ORDER BY clause */
    ref WhereCost pCost         /* Lowest cost query plan */
    )
    {
#if !SQLITE_OMIT_VIRTUALTABLE
      if ( IsVirtual( pSrc.pTab ) )
      {
        sqlite3_index_info p = null;
        bestVirtualIndex( pParse, pWC, pSrc, notReady, notValid, pOrderBy, ref pCost, ref p );
        if ( p.needToFreeIdxStr != 0 )
        {
          //sqlite3_free(ref p.idxStr);
        }
        sqlite3DbFree( pParse.db, ref p );
      }
      else
#endif
      {
        bestBtreeIndex( pParse, pWC, pSrc, notReady, notValid, pOrderBy, ref pCost );
      }
    }

    /*
    ** Disable a term in the WHERE clause.  Except, do not disable the term
    ** if it controls a LEFT OUTER JOIN and it did not originate in the ON
    ** or USING clause of that join.
    **
    ** Consider the term t2.z='ok' in the following queries:
    **
    **   (1)  SELECT * FROM t1 LEFT JOIN t2 ON t1.a=t2.x WHERE t2.z='ok'
    **   (2)  SELECT * FROM t1 LEFT JOIN t2 ON t1.a=t2.x AND t2.z='ok'
    **   (3)  SELECT * FROM t1, t2 WHERE t1.a=t2.x AND t2.z='ok'
    **
    ** The t2.z='ok' is disabled in the in (2) because it originates
    ** in the ON clause.  The term is disabled in (3) because it is not part
    ** of a LEFT OUTER JOIN.  In (1), the term is not disabled.
    **
    ** IMPLEMENTATION-OF: R-24597-58655 No tests are done for terms that are
    ** completely satisfied by indices.
    **
    ** Disabling a term causes that term to not be tested in the inner loop
    ** of the join.  Disabling is an optimization.  When terms are satisfied
    ** by indices, we disable them to prevent redundant tests in the inner
    ** loop.  We would get the correct results if nothing were ever disabled,
    ** but joins might run a little slower.  The trick is to disable as much
    ** as we can without disabling too much.  If we disabled in (1), we'd get
    ** the wrong answer.  See ticket #813.
    */
    static void disableTerm( WhereLevel pLevel, WhereTerm pTerm )
    {
      if ( pTerm != null
      && ( pTerm.wtFlags & TERM_CODED ) == 0
      && ( pLevel.iLeftJoin == 0 || ExprHasProperty( pTerm.pExpr, EP_FromJoin ) ) )
      {
        pTerm.wtFlags |= TERM_CODED;
        if ( pTerm.iParent >= 0 )
        {
          WhereTerm pOther = pTerm.pWC.a[pTerm.iParent];
          if ( ( --pOther.nChild ) == 0 )
          {
            disableTerm( pLevel, pOther );
          }
        }
      }
    }

    /*
    ** Code an OP_Affinity opcode to apply the column affinity string zAff
    ** to the n registers starting at base. 
    **
    ** As an optimization, SQLITE_AFF_NONE entries (which are no-ops) at the
    ** beginning and end of zAff are ignored.  If all entries in zAff are
    ** SQLITE_AFF_NONE, then no code gets generated.
    **
    ** This routine makes its own copy of zAff so that the caller is free
    ** to modify zAff after this routine returns.
    */
    static void codeApplyAffinity( Parse pParse, int _base, int n, string zAff )
    {
      Vdbe v = pParse.pVdbe;
      //if (zAff == 0)
      //{
      //  Debug.Assert(pParse.db.mallocFailed);
      //  return;
      //}
      Debug.Assert( v != null );
      /* Adjust base and n to skip over SQLITE_AFF_NONE entries at the beginning
      ** and end of the affinity string.
      */
      while ( n > 0 && zAff[0] == SQLITE_AFF_NONE )
      {
        n--;
        _base++;
        zAff = zAff.Substring( 1 );// zAff++;
      }
      while ( n > 1 && zAff[n - 1] == SQLITE_AFF_NONE )
      {
        n--;
      }

      /* Code the OP_Affinity opcode if there is anything left to do. */
      if ( n > 0 )
      {
        sqlite3VdbeAddOp2( v, OP_Affinity, _base, n );
        sqlite3VdbeChangeP4( v, -1, zAff, n );
        sqlite3ExprCacheAffinityChange( pParse, _base, n );
      }
    }

    /*
    ** Generate code for a single equality term of the WHERE clause.  An equality
    ** term can be either X=expr or X IN (...).   pTerm is the term to be
    ** coded.
    **
    ** The current value for the constraint is left in register iReg.
    **
    ** For a constraint of the form X=expr, the expression is evaluated and its
    ** result is left on the stack.  For constraints of the form X IN (...)
    ** this routine sets up a loop that will iterate over all values of X.
    */
    static int codeEqualityTerm(
    Parse pParse,      /* The parsing context */
    WhereTerm pTerm,   /* The term of the WHERE clause to be coded */
    WhereLevel pLevel, /* When level of the FROM clause we are working on */
    int iTarget         /* Attempt to leave results in this register */
    )
    {
      Expr pX = pTerm.pExpr;
      Vdbe v = pParse.pVdbe;
      int iReg;                  /* Register holding results */

      Debug.Assert( iTarget > 0 );
      if ( pX.op == TK_EQ )
      {
        iReg = sqlite3ExprCodeTarget( pParse, pX.pRight, iTarget );
      }
      else if ( pX.op == TK_ISNULL )
      {
        iReg = iTarget;
        sqlite3VdbeAddOp2( v, OP_Null, 0, iReg );
#if  !SQLITE_OMIT_SUBQUERY
      }
      else
      {
        int eType;
        int iTab;
        InLoop pIn;

        Debug.Assert( pX.op == TK_IN );
        iReg = iTarget;
        int iDummy = -1;
        eType = sqlite3FindInIndex( pParse, pX, ref iDummy );
        iTab = pX.iTable;
        sqlite3VdbeAddOp2( v, OP_Rewind, iTab, 0 );
        Debug.Assert( ( pLevel.plan.wsFlags & WHERE_IN_ABLE ) != 0 );
        if ( pLevel.u._in.nIn == 0 )
        {
          pLevel.addrNxt = sqlite3VdbeMakeLabel( v );
        }
        pLevel.u._in.nIn++;
        if ( pLevel.u._in.aInLoop == null )
          pLevel.u._in.aInLoop = new InLoop[pLevel.u._in.nIn];
        else
          Array.Resize( ref pLevel.u._in.aInLoop, pLevel.u._in.nIn );
        //sqlite3DbReallocOrFree(pParse.db, pLevel.u._in.aInLoop,
        //                       sizeof(pLevel.u._in.aInLoop[0])*pLevel.u._in.nIn);
        //pIn = pLevel.u._in.aInLoop;
        if ( pLevel.u._in.aInLoop != null )//(pIn )
        {
          pLevel.u._in.aInLoop[pLevel.u._in.nIn - 1] = new InLoop();
          pIn = pLevel.u._in.aInLoop[pLevel.u._in.nIn - 1];//pIn++
          pIn.iCur = iTab;
          if ( eType == IN_INDEX_ROWID )
          {
            pIn.addrInTop = sqlite3VdbeAddOp2( v, OP_Rowid, iTab, iReg );
          }
          else
          {
            pIn.addrInTop = sqlite3VdbeAddOp3( v, OP_Column, iTab, 0, iReg );
          }
          sqlite3VdbeAddOp1( v, OP_IsNull, iReg );
        }
        else
        {
          pLevel.u._in.nIn = 0;
        }
#endif
      }
      disableTerm( pLevel, pTerm );
      return iReg;
    }

    /*
    ** Generate code for a single equality term of the WHERE clause.  An equality
    ** term can be either X=expr or X IN (...).   pTerm is the term to be 
    ** coded.
    **
    ** For example, consider table t1(a,b,c,d,e,f) with index i1(a,b,c).
    ** Suppose the WHERE clause is this:  a==5 AND b IN (1,2,3) AND c>5 AND c<10
    ** The index has as many as three equality constraints, but in this
    ** example, the third "c" value is an inequality.  So only two
    ** constraints are coded.  This routine will generate code to evaluate
    ** a==5 and b IN (1,2,3).  The current values for a and b will be stored
    ** in consecutive registers and the index of the first register is returned.
    **
    ** In the example above nEq==2.  But this subroutine works for any value
    ** of nEq including 0.  If nEq==null, this routine is nearly a no-op.
    ** The only thing it does is allocate the pLevel.iMem memory cell and
    ** compute the affinity string.
    **
    ** This routine always allocates at least one memory cell and returns
    ** the index of that memory cell. The code that
    ** calls this routine will use that memory cell to store the termination
    ** key value of the loop.  If one or more IN operators appear, then
    ** this routine allocates an additional nEq memory cells for internal
    ** use.
    **
    ** Before returning, *pzAff is set to point to a buffer containing a
    ** copy of the column affinity string of the index allocated using
    ** sqlite3DbMalloc(). Except, entries in the copy of the string associated
    ** with equality constraints that use NONE affinity are set to
    ** SQLITE_AFF_NONE. This is to deal with SQL such as the following:
    **
    **   CREATE TABLE t1(a TEXT PRIMARY KEY, b);
    **   SELECT ... FROM t1 AS t2, t1 WHERE t1.a = t2.b;
    **
    ** In the example above, the index on t1(a) has TEXT affinity. But since
    ** the right hand side of the equality constraint (t2.b) has NONE affinity,
    ** no conversion should be attempted before using a t2.b value as part of
    ** a key to search the index. Hence the first byte in the returned affinity
    ** string in this example would be set to SQLITE_AFF_NONE.
    */
    static int codeAllEqualityTerms(
    Parse pParse,        /* Parsing context */
    WhereLevel pLevel,   /* Which nested loop of the FROM we are coding */
    WhereClause pWC,     /* The WHERE clause */
    Bitmask notReady,    /* Which parts of FROM have not yet been coded */
    int nExtraReg,       /* Number of extra registers to allocate */
    out StringBuilder pzAff /* OUT: Set to point to affinity string */
    )
    {
      int nEq = (int)pLevel.plan.nEq;   /* The number of == or IN constraints to code */
      Vdbe v = pParse.pVdbe;       /* The vm under construction */
      Index pIdx;                  /* The index being used for this loop */
      int iCur = pLevel.iTabCur;   /* The cursor of the table */
      WhereTerm pTerm;             /* A single constraint term */
      int j;                       /* Loop counter */
      int regBase;                 /* Base register */
      int nReg;                    /* Number of registers to allocate */
      StringBuilder zAff;          /* Affinity string to return */

      /* This module is only called on query plans that use an index. */
      Debug.Assert( ( pLevel.plan.wsFlags & WHERE_INDEXED ) != 0 );
      pIdx = pLevel.plan.u.pIdx;

      /* Figure out how many memory cells we will need then allocate them.
      */
      regBase = pParse.nMem + 1;
      nReg = (int)( pLevel.plan.nEq + nExtraReg );
      pParse.nMem += nReg;

      zAff = new StringBuilder( sqlite3IndexAffinityStr( v, pIdx ) );//sqlite3DbStrDup(pParse.db, sqlite3IndexAffinityStr(v, pIdx));
      //if( null==zAff ){
      //  pParse.db.mallocFailed = 1;
      //}

      /* Evaluate the equality constraints
      */
      Debug.Assert( pIdx.nColumn >= nEq );
      for ( j = 0; j < nEq; j++ )
      {
        int r1;
        int k = pIdx.aiColumn[j];
        pTerm = findTerm( pWC, iCur, k, notReady, pLevel.plan.wsFlags, pIdx );
        if ( NEVER( pTerm == null ) )
          break;
        /* The following true for indices with redundant columns. 
        ** Ex: CREATE INDEX i1 ON t1(a,b,a); SELECT * FROM t1 WHERE a=0 AND b=0; */
        testcase( ( pTerm.wtFlags & TERM_CODED ) != 0 );
        testcase( pTerm.wtFlags & TERM_VIRTUAL ); /* EV: R-30575-11662 */
        r1 = codeEqualityTerm( pParse, pTerm, pLevel, regBase + j );
        if ( r1 != regBase + j )
        {
          if ( nReg == 1 )
          {
            sqlite3ReleaseTempReg( pParse, regBase );
            regBase = r1;
          }
          else
          {
            sqlite3VdbeAddOp2( v, OP_SCopy, r1, regBase + j );
          }
        }
        testcase( pTerm.eOperator & WO_ISNULL );
        testcase( pTerm.eOperator & WO_IN );
        if ( ( pTerm.eOperator & ( WO_ISNULL | WO_IN ) ) == 0 )
        {
          Expr pRight = pTerm.pExpr.pRight;
          sqlite3ExprCodeIsNullJump( v, pRight, regBase + j, pLevel.addrBrk );
          if ( zAff.Length > 0 )
          {
            if ( sqlite3CompareAffinity( pRight, zAff[j] ) == SQLITE_AFF_NONE )
            {
              zAff[j] = SQLITE_AFF_NONE;
            }
            if ( ( sqlite3ExprNeedsNoAffinityChange( pRight, zAff[j] ) ) != 0 )
            {
              zAff[j] = SQLITE_AFF_NONE;
            }
          }
        }
      }
      pzAff = zAff;
      return regBase;
    }

#if !SQLITE_OMIT_EXPLAIN
    /*
** This routine is a helper for explainIndexRange() below
**
** pStr holds the text of an expression that we are building up one term
** at a time.  This routine adds a new term to the end of the expression.
** Terms are separated by AND so add the "AND" text for second and subsequent
** terms only.
*/
    static void explainAppendTerm(
    StrAccum pStr,              /* The text expression being built */
    int iTerm,                  /* Index of this term.  First is zero */
    string zColumn,             /* Name of the column */
    string zOp                  /* Name of the operator */
    )
    {
      if ( iTerm != 0 )
        sqlite3StrAccumAppend( pStr, " AND ", 5 );
      sqlite3StrAccumAppend( pStr, zColumn, -1 );
      sqlite3StrAccumAppend( pStr, zOp, 1 );
      sqlite3StrAccumAppend( pStr, "?", 1 );
    }

    /*
    ** Argument pLevel describes a strategy for scanning table pTab. This 
    ** function returns a pointer to a string buffer containing a description
    ** of the subset of table rows scanned by the strategy in the form of an
    ** SQL expression. Or, if all rows are scanned, NULL is returned.
    **
    ** For example, if the query:
    **
    **   SELECT * FROM t1 WHERE a=1 AND b>2;
    **
    ** is run and there is an index on (a, b), then this function returns a
    ** string similar to:
    **
    **   "a=? AND b>?"
    **
    ** The returned pointer points to memory obtained from sqlite3DbMalloc().
    ** It is the responsibility of the caller to free the buffer when it is
    ** no longer required.
    */
    static string explainIndexRange( sqlite3 db, WhereLevel pLevel, Table pTab )
    {
      WherePlan pPlan = pLevel.plan;
      Index pIndex = pPlan.u.pIdx;
      uint nEq = pPlan.nEq;
      int i, j;
      Column[] aCol = pTab.aCol;
      int[] aiColumn = pIndex.aiColumn;
      StrAccum txt = new StrAccum( 100 );

      if ( nEq == 0 && ( pPlan.wsFlags & ( WHERE_BTM_LIMIT | WHERE_TOP_LIMIT ) ) == 0 )
      {
        return null;
      }
      sqlite3StrAccumInit( txt, null, 0, SQLITE_MAX_LENGTH );
      txt.db = db;
      sqlite3StrAccumAppend( txt, " (", 2 );
      for ( i = 0; i < nEq; i++ )
      {
        explainAppendTerm( txt, i, aCol[aiColumn[i]].zName, "=" );
      }

      j = i;
      if ( ( pPlan.wsFlags & WHERE_BTM_LIMIT ) != 0 )
      {
        explainAppendTerm( txt, i++, aCol[aiColumn[j]].zName, ">" );
      }
      if ( ( pPlan.wsFlags & WHERE_TOP_LIMIT ) != 0 )
      {
        explainAppendTerm( txt, i, aCol[aiColumn[j]].zName, "<" );
      }
      sqlite3StrAccumAppend( txt, ")", 1 );
      return sqlite3StrAccumFinish( txt );
    }

    /*
    ** This function is a no-op unless currently processing an EXPLAIN QUERY PLAN
    ** command. If the query being compiled is an EXPLAIN QUERY PLAN, a single
    ** record is added to the output to describe the table scan strategy in 
    ** pLevel.
    */
    static void explainOneScan(
    Parse pParse,                   /* Parse context */
    SrcList pTabList,               /* Table list this loop refers to */
    WhereLevel pLevel,              /* Scan to write OP_Explain opcode for */
    int iLevel,                     /* Value for "level" column of output */
    int iFrom,                      /* Value for "from" column of output */
    u16 wctrlFlags                  /* Flags passed to sqlite3WhereBegin() */
    )
    {
      if ( pParse.explain == 2 )
      {
        u32 flags = pLevel.plan.wsFlags;
        SrcList_item pItem = pTabList.a[pLevel.iFrom];
        Vdbe v = pParse.pVdbe;       /* VM being constructed */
        sqlite3 db = pParse.db;      /* Database handle */
        StringBuilder zMsg = new StringBuilder( 1000 ); /* Text to add to EQP output */
        sqlite3_int64 nRow;          /* Expected number of rows visited by scan */
        int iId = pParse.iSelectId;  /* Select id (left-most output column) */
        bool isSearch;               /* True for a SEARCH. False for SCAN. */

        if ( ( flags & WHERE_MULTI_OR ) != 0 || ( wctrlFlags & WHERE_ONETABLE_ONLY ) != 0 )
          return;

        isSearch = ( pLevel.plan.nEq > 0 )
        || ( flags & ( WHERE_BTM_LIMIT | WHERE_TOP_LIMIT ) ) != 0
        || ( wctrlFlags & ( WHERE_ORDERBY_MIN | WHERE_ORDERBY_MAX ) ) != 0;

        zMsg.Append( sqlite3MPrintf( db, "%s", isSearch ? "SEARCH" : "SCAN" ) );
        if ( pItem.pSelect != null )
        {
          zMsg.Append( sqlite3MAppendf( db, null, " SUBQUERY %d", pItem.iSelectId ) );
        }
        else
        {
          zMsg.Append( sqlite3MAppendf( db, null, " TABLE %s", pItem.zName ) );
        }

        if ( pItem.zAlias != null )
        {
          zMsg.Append( sqlite3MAppendf( db, null, " AS %s", pItem.zAlias ) );
        }
        if ( ( flags & WHERE_INDEXED ) != 0 )
        {
          string zWhere = explainIndexRange( db, pLevel, pItem.pTab );
          zMsg.Append( sqlite3MAppendf( db, null, " USING %s%sINDEX%s%s%s",
          ( ( flags & WHERE_TEMP_INDEX ) != 0 ? "AUTOMATIC " : string.Empty ),
          ( ( flags & WHERE_IDX_ONLY ) != 0 ? "COVERING " : string.Empty ),
          ( ( flags & WHERE_TEMP_INDEX ) != 0 ? string.Empty : " " ),
          ( ( flags & WHERE_TEMP_INDEX ) != 0 ? string.Empty : pLevel.plan.u.pIdx.zName ),
          zWhere ?? string.Empty
          ) );
          sqlite3DbFree( db, ref zWhere );
        }
        else if ( ( flags & ( WHERE_ROWID_EQ | WHERE_ROWID_RANGE ) ) != 0 )
        {
          zMsg.Append( " USING INTEGER PRIMARY KEY" );

          if ( ( flags & WHERE_ROWID_EQ ) != 0 )
          {
            zMsg.Append( " (rowid=?)" );
          }
          else if ( ( flags & WHERE_BOTH_LIMIT ) == WHERE_BOTH_LIMIT )
          {
            zMsg.Append( " (rowid>? AND rowid<?)" );
          }
          else if ( ( flags & WHERE_BTM_LIMIT ) != 0 )
          {
            zMsg.Append( " (rowid>?)" );
          }
          else if ( ( flags & WHERE_TOP_LIMIT ) != 0 )
          {
            zMsg.Append( " (rowid<?)" );
          }
        }
#if !SQLITE_OMIT_VIRTUALTABLE
        else if ( ( flags & WHERE_VIRTUALTABLE ) != 0 )
        {
          sqlite3_index_info pVtabIdx = pLevel.plan.u.pVtabIdx;
          zMsg.Append( sqlite3MAppendf( db, null, " VIRTUAL TABLE INDEX %d:%s",
          pVtabIdx.idxNum, pVtabIdx.idxStr ) );
        }
#endif
        if ( ( wctrlFlags & ( WHERE_ORDERBY_MIN | WHERE_ORDERBY_MAX ) ) != 0 )
        {
          testcase( wctrlFlags & WHERE_ORDERBY_MIN );
          nRow = 1;
        }
        else
        {
          nRow = (sqlite3_int64)pLevel.plan.nRow;
        }
        zMsg.Append( sqlite3MAppendf( db, null, " (~%lld rows)", nRow ) );
        sqlite3VdbeAddOp4( v, OP_Explain, iId, iLevel, iFrom, zMsg, P4_DYNAMIC );
      }
    }
#else
//# define explainOneScan(u,v,w,x,y,z)
static void explainOneScan(  Parse u,  SrcList v,  WhereLevel w,  int x,  int y,  u16 z){}
#endif //* SQLITE_OMIT_EXPLAIN */


    /*
** Generate code for the start of the iLevel-th loop in the WHERE clause
** implementation described by pWInfo.
*/
    static Bitmask codeOneLoopStart(
    WhereInfo pWInfo,     /* Complete information about the WHERE clause */
    int iLevel,           /* Which level of pWInfo.a[] should be coded */
    u16 wctrlFlags,       /* One of the WHERE_* flags defined in sqliteInt.h */
    Bitmask notReady      /* Which tables are currently available */
    )
    {
      int j, k;                 /* Loop counters */
      int iCur;                 /* The VDBE cursor for the table */
      int addrNxt;              /* Where to jump to continue with the next IN case */
      int omitTable;            /* True if we use the index only */
      int bRev;                 /* True if we need to scan in reverse order */
      WhereLevel pLevel;        /* The where level to be coded */
      WhereClause pWC;          /* Decomposition of the entire WHERE clause */
      WhereTerm pTerm;          /* A WHERE clause term */
      Parse pParse;             /* Parsing context */
      Vdbe v;                   /* The prepared stmt under constructions */
      SrcList_item pTabItem;    /* FROM clause term being coded */
      int addrBrk;              /* Jump here to break out of the loop */
      int addrCont;             /* Jump here to continue with next cycle */
      int iRowidReg = 0;        /* Rowid is stored in this register, if not zero */
      int iReleaseReg = 0;      /* Temp register to free before returning */

      pParse = pWInfo.pParse;
      v = pParse.pVdbe;
      pWC = pWInfo.pWC;
      pLevel = pWInfo.a[iLevel];
      pTabItem = pWInfo.pTabList.a[pLevel.iFrom];
      iCur = pTabItem.iCursor;
      bRev = ( pLevel.plan.wsFlags & WHERE_REVERSE ) != 0 ? 1 : 0;
      omitTable = ( ( pLevel.plan.wsFlags & WHERE_IDX_ONLY ) != 0
      && ( wctrlFlags & WHERE_FORCE_TABLE ) == 0 ) ? 1 : 0;

      /* Create labels for the "break" and "continue" instructions
      ** for the current loop.  Jump to addrBrk to break out of a loop.
      ** Jump to cont to go immediately to the next iteration of the
      ** loop.
      **
      ** When there is an IN operator, we also have a "addrNxt" label that
      ** means to continue with the next IN value combination.  When
      ** there are no IN operators in the constraints, the "addrNxt" label
      ** is the same as "addrBrk".
      */
      addrBrk = pLevel.addrBrk = pLevel.addrNxt = sqlite3VdbeMakeLabel( v );
      addrCont = pLevel.addrCont = sqlite3VdbeMakeLabel( v );

      /* If this is the right table of a LEFT OUTER JOIN, allocate and
      ** initialize a memory cell that records if this table matches any
      ** row of the left table of the join.
      */
      if ( pLevel.iFrom > 0 && ( pTabItem.jointype & JT_LEFT ) != 0 )// Check value of pTabItem[0].jointype
      {
        pLevel.iLeftJoin = ++pParse.nMem;
        sqlite3VdbeAddOp2( v, OP_Integer, 0, pLevel.iLeftJoin );
#if SQLITE_DEBUG
        VdbeComment( v, "init LEFT JOIN no-match flag" );
#endif
      }

#if  !SQLITE_OMIT_VIRTUALTABLE
      if ( ( pLevel.plan.wsFlags & WHERE_VIRTUALTABLE ) != 0 )
      {
        /* Case 0:  The table is a virtual-table.  Use the VFilter and VNext
        **          to access the data.
        */
        int iReg;   /* P3 Value for OP_VFilter */
        sqlite3_index_info pVtabIdx = pLevel.plan.u.pVtabIdx;
        int nConstraint = pVtabIdx.nConstraint;
        sqlite3_index_constraint_usage[] aUsage = pVtabIdx.aConstraintUsage;
        sqlite3_index_constraint[] aConstraint = pVtabIdx.aConstraint;

        sqlite3ExprCachePush( pParse );
        iReg = sqlite3GetTempRange( pParse, nConstraint + 2 );
        for ( j = 1; j <= nConstraint; j++ )
        {
          for ( k = 0; k < nConstraint; k++ )
          {
            if ( aUsage[k].argvIndex == j )
            {
              int iTerm = aConstraint[k].iTermOffset;
              sqlite3ExprCode( pParse, pWC.a[iTerm].pExpr.pRight, iReg + j + 1 );
              break;
            }
          }
          if ( k == nConstraint )
            break;
        }
        sqlite3VdbeAddOp2( v, OP_Integer, pVtabIdx.idxNum, iReg );
        sqlite3VdbeAddOp2( v, OP_Integer, j - 1, iReg + 1 );
        sqlite3VdbeAddOp4( v, OP_VFilter, iCur, addrBrk, iReg, pVtabIdx.idxStr,
        pVtabIdx.needToFreeIdxStr != 0 ? P4_MPRINTF : P4_STATIC );
        pVtabIdx.needToFreeIdxStr = 0;
        for ( j = 0; j < nConstraint; j++ )
        {
          if ( aUsage[j].omit != false )
          {
            int iTerm = aConstraint[j].iTermOffset;
            disableTerm( pLevel, pWC.a[iTerm] );
          }
        }
        pLevel.op = OP_VNext;
        pLevel.p1 = iCur;
        pLevel.p2 = sqlite3VdbeCurrentAddr( v );
        sqlite3ReleaseTempRange( pParse, iReg, nConstraint + 2 );
        sqlite3ExprCachePop( pParse, 1 );
      }
      else
#endif //* SQLITE_OMIT_VIRTUALTABLE */

        if ( ( pLevel.plan.wsFlags & WHERE_ROWID_EQ ) != 0 )
        {
          /* Case 1:  We can directly reference a single row using an
          **          equality comparison against the ROWID field.  Or
          **          we reference multiple rows using a "rowid IN (...)"
          **          construct.
          */
          iReleaseReg = sqlite3GetTempReg( pParse );
          pTerm = findTerm( pWC, iCur, -1, notReady, WO_EQ | WO_IN, null );
          Debug.Assert( pTerm != null );
          Debug.Assert( pTerm.pExpr != null );
          Debug.Assert( pTerm.leftCursor == iCur );
          Debug.Assert( omitTable == 0 );
          testcase( pTerm.wtFlags & TERM_VIRTUAL ); /* EV: R-30575-11662 */
          iRowidReg = codeEqualityTerm( pParse, pTerm, pLevel, iReleaseReg );
          addrNxt = pLevel.addrNxt;
          sqlite3VdbeAddOp2( v, OP_MustBeInt, iRowidReg, addrNxt );
          sqlite3VdbeAddOp3( v, OP_NotExists, iCur, addrNxt, iRowidReg );
          sqlite3ExprCacheStore( pParse, iCur, -1, iRowidReg );
#if SQLITE_DEBUG
          VdbeComment( v, "pk" );
#endif
          pLevel.op = OP_Noop;
        }
        else if ( ( pLevel.plan.wsFlags & WHERE_ROWID_RANGE ) != 0 )
        {
          /* Case 2:  We have an inequality comparison against the ROWID field.
          */
          int testOp = OP_Noop;
          int start;
          int memEndValue = 0;
          WhereTerm pStart, pEnd;

          Debug.Assert( omitTable == 0 );
          pStart = findTerm( pWC, iCur, -1, notReady, WO_GT | WO_GE, null );
          pEnd = findTerm( pWC, iCur, -1, notReady, WO_LT | WO_LE, null );
          if ( bRev != 0 )
          {
            pTerm = pStart;
            pStart = pEnd;
            pEnd = pTerm;
          }
          if ( pStart != null )
          {
            Expr pX;             /* The expression that defines the start bound */
            int r1, rTemp = 0;        /* Registers for holding the start boundary */

            /* The following constant maps TK_xx codes into corresponding
            ** seek opcodes.  It depends on a particular ordering of TK_xx
            */
            u8[] aMoveOp = new u8[]{
/* TK_GT */  OP_SeekGt,
/* TK_LE */  OP_SeekLe,
/* TK_LT */  OP_SeekLt,
/* TK_GE */  OP_SeekGe
};
            Debug.Assert( TK_LE == TK_GT + 1 );      /* Make sure the ordering.. */
            Debug.Assert( TK_LT == TK_GT + 2 );      /*  ... of the TK_xx values... */
            Debug.Assert( TK_GE == TK_GT + 3 );      /*  ... is correcct. */

            testcase( pStart.wtFlags & TERM_VIRTUAL ); /* EV: R-30575-11662 */
            pX = pStart.pExpr;
            Debug.Assert( pX != null );
            Debug.Assert( pStart.leftCursor == iCur );
            r1 = sqlite3ExprCodeTemp( pParse, pX.pRight, ref rTemp );
            sqlite3VdbeAddOp3( v, aMoveOp[pX.op - TK_GT], iCur, addrBrk, r1 );
#if SQLITE_DEBUG
            VdbeComment( v, "pk" );
#endif
            sqlite3ExprCacheAffinityChange( pParse, r1, 1 );
            sqlite3ReleaseTempReg( pParse, rTemp );
            disableTerm( pLevel, pStart );
          }
          else
          {
            sqlite3VdbeAddOp2( v, bRev != 0 ? OP_Last : OP_Rewind, iCur, addrBrk );
          }
          if ( pEnd != null )
          {
            Expr pX;
            pX = pEnd.pExpr;
            Debug.Assert( pX != null );
            Debug.Assert( pEnd.leftCursor == iCur );
            testcase( pEnd.wtFlags & TERM_VIRTUAL ); /* EV: R-30575-11662 */
            memEndValue = ++pParse.nMem;
            sqlite3ExprCode( pParse, pX.pRight, memEndValue );
            if ( pX.op == TK_LT || pX.op == TK_GT )
            {
              testOp = bRev != 0 ? OP_Le : OP_Ge;
            }
            else
            {
              testOp = bRev != 0 ? OP_Lt : OP_Gt;
            }
            disableTerm( pLevel, pEnd );
          }
          start = sqlite3VdbeCurrentAddr( v );
          pLevel.op = (u8)( bRev != 0 ? OP_Prev : OP_Next );
          pLevel.p1 = iCur;
          pLevel.p2 = start;
          if ( pStart == null && pEnd == null )
          {
            pLevel.p5 = SQLITE_STMTSTATUS_FULLSCAN_STEP;
          }
          else
          {
            Debug.Assert( pLevel.p5 == 0 );
          }
          if ( testOp != OP_Noop )
          {
            iRowidReg = iReleaseReg = sqlite3GetTempReg( pParse );
            sqlite3VdbeAddOp2( v, OP_Rowid, iCur, iRowidReg );
            sqlite3ExprCacheStore( pParse, iCur, -1, iRowidReg );
            sqlite3VdbeAddOp3( v, testOp, memEndValue, addrBrk, iRowidReg );
            sqlite3VdbeChangeP5( v, SQLITE_AFF_NUMERIC | SQLITE_JUMPIFNULL );
          }
        }
        else if ( ( pLevel.plan.wsFlags & ( WHERE_COLUMN_RANGE | WHERE_COLUMN_EQ ) ) != 0 )
        {
          /* Case 3: A scan using an index.
          **
          **         The WHERE clause may contain zero or more equality
          **         terms ("==" or "IN" operators) that refer to the N
          **         left-most columns of the index. It may also contain
          **         inequality constraints (>, <, >= or <=) on the indexed
          **         column that immediately follows the N equalities. Only
          **         the right-most column can be an inequality - the rest must
          **         use the "==" and "IN" operators. For example, if the
          **         index is on (x,y,z), then the following clauses are all
          **         optimized:
          **
          **            x=5
          **            x=5 AND y=10
          **            x=5 AND y<10
          **            x=5 AND y>5 AND y<10
          **            x=5 AND y=5 AND z<=10
          **
          **         The z<10 term of the following cannot be used, only
          **         the x=5 term:
          **
          **            x=5 AND z<10
          **
          **         N may be zero if there are inequality constraints.
          **         If there are no inequality constraints, then N is at
          **         least one.
          **
          **         This case is also used when there are no WHERE clause
          **         constraints but an index is selected anyway, in order
          **         to force the output order to conform to an ORDER BY.
          */
          u8[] aStartOp = new u8[]  {
0,
0,
OP_Rewind,           /* 2: (!start_constraints && startEq &&  !bRev) */
OP_Last,             /* 3: (!start_constraints && startEq &&   bRev) */
OP_SeekGt,           /* 4: (start_constraints  && !startEq && !bRev) */
OP_SeekLt,           /* 5: (start_constraints  && !startEq &&  bRev) */
OP_SeekGe,           /* 6: (start_constraints  &&  startEq && !bRev) */
OP_SeekLe            /* 7: (start_constraints  &&  startEq &&  bRev) */
};
          u8[] aEndOp = new u8[]  {
OP_Noop,             /* 0: (!end_constraints) */
OP_IdxGE,            /* 1: (end_constraints && !bRev) */
OP_IdxLT             /* 2: (end_constraints && bRev) */
};
          int nEq = (int)pLevel.plan.nEq; /* Number of == or IN terms */
          int isMinQuery = 0;          /* If this is an optimized SELECT min(x).. */
          int regBase;                 /* Base register holding constraint values */
          int r1;                      /* Temp register */
          WhereTerm pRangeStart = null;  /* Inequality constraint at range start */
          WhereTerm pRangeEnd = null;    /* Inequality constraint at range end */
          int startEq;                   /* True if range start uses ==, >= or <= */
          int endEq;                     /* True if range end uses ==, >= or <= */
          int start_constraints;         /* Start of range is constrained */
          int nConstraint;               /* Number of constraint terms */
          Index pIdx;                    /* The index we will be using */
          int iIdxCur;                   /* The VDBE cursor for the index */
          int nExtraReg = 0;             /* Number of extra registers needed */
          int op;                        /* Instruction opcode */
          StringBuilder zStartAff = new StringBuilder();
          ;/* Affinity for start of range constraint */
          StringBuilder zEndAff;         /* Affinity for end of range constraint */

          pIdx = pLevel.plan.u.pIdx;
          iIdxCur = pLevel.iIdxCur;
          k = pIdx.aiColumn[nEq];        /* Column for inequality constraints */

          /* If this loop satisfies a sort order (pOrderBy) request that
          ** was pDebug.Assed to this function to implement a "SELECT min(x) ..."
          ** query, then the caller will only allow the loop to run for
          ** a single iteration. This means that the first row returned
          ** should not have a NULL value stored in 'x'. If column 'x' is
          ** the first one after the nEq equality constraints in the index,
          ** this requires some special handling.
          */
          if ( ( wctrlFlags & WHERE_ORDERBY_MIN ) != 0
          && ( ( pLevel.plan.wsFlags & WHERE_ORDERBY ) != 0 )
          && ( pIdx.nColumn > nEq )
          )
          {
            /* Debug.Assert( pOrderBy.nExpr==1 ); */
            /* Debug.Assert( pOrderBy.a[0].pExpr.iColumn==pIdx.aiColumn[nEq] ); */
            isMinQuery = 1;
            nExtraReg = 1;
          }

          /* Find any inequality constraint terms for the start and end
          ** of the range.
          */
          if ( ( pLevel.plan.wsFlags & WHERE_TOP_LIMIT ) != 0 )
          {
            pRangeEnd = findTerm( pWC, iCur, k, notReady, ( WO_LT | WO_LE ), pIdx );
            nExtraReg = 1;
          }
          if ( ( pLevel.plan.wsFlags & WHERE_BTM_LIMIT ) != 0 )
          {
            pRangeStart = findTerm( pWC, iCur, k, notReady, ( WO_GT | WO_GE ), pIdx );
            nExtraReg = 1;
          }

          /* Generate code to evaluate all constraint terms using == or IN
          ** and store the values of those terms in an array of registers
          ** starting at regBase.
          */
          regBase = codeAllEqualityTerms(
          pParse, pLevel, pWC, notReady, nExtraReg, out zStartAff
          );
          zEndAff = new StringBuilder( zStartAff.ToString() );//sqlite3DbStrDup(pParse.db, zStartAff);
          addrNxt = pLevel.addrNxt;

          /* If we are doing a reverse order scan on an ascending index, or
          ** a forward order scan on a descending index, interchange the
          ** start and end terms (pRangeStart and pRangeEnd).
          */
          if ( nEq < pIdx.nColumn && bRev == ( pIdx.aSortOrder[nEq] == SQLITE_SO_ASC ? 1 : 0 ) )
          {
            SWAP( ref pRangeEnd, ref pRangeStart );
          }

          testcase( pRangeStart != null && ( pRangeStart.eOperator & WO_LE ) != 0 );
          testcase( pRangeStart != null && ( pRangeStart.eOperator & WO_GE ) != 0 );
          testcase( pRangeEnd != null && ( pRangeEnd.eOperator & WO_LE ) != 0 );
          testcase( pRangeEnd != null && ( pRangeEnd.eOperator & WO_GE ) != 0 );
          startEq = ( null == pRangeStart || ( pRangeStart.eOperator & ( WO_LE | WO_GE ) ) != 0 ) ? 1 : 0;
          endEq = ( null == pRangeEnd || ( pRangeEnd.eOperator & ( WO_LE | WO_GE ) ) != 0 ) ? 1 : 0;
          start_constraints = ( pRangeStart != null || nEq > 0 ) ? 1 : 0;

          /* Seek the index cursor to the start of the range. */
          nConstraint = nEq;
          if ( pRangeStart != null )
          {
            Expr pRight = pRangeStart.pExpr.pRight;
            sqlite3ExprCode( pParse, pRight, regBase + nEq );
            if ( ( pRangeStart.wtFlags & TERM_VNULL ) == 0 )
            {
              sqlite3ExprCodeIsNullJump( v, pRight, regBase + nEq, addrNxt );
            }
            if ( zStartAff.Length != 0 )
            {
              if ( sqlite3CompareAffinity( pRight, zStartAff[nEq] ) == SQLITE_AFF_NONE )
              {
                /* Since the comparison is to be performed with no conversions
                ** applied to the operands, set the affinity to apply to pRight to 
                ** SQLITE_AFF_NONE.  */
                zStartAff[nEq] = SQLITE_AFF_NONE;
              }
              if ( ( sqlite3ExprNeedsNoAffinityChange( pRight, zStartAff[nEq] ) ) != 0 )
              {
                zStartAff[nEq] = SQLITE_AFF_NONE;
              }
            }
            nConstraint++;
            testcase( pRangeStart.wtFlags & TERM_VIRTUAL ); /* EV: R-30575-11662 */
          }
          else if ( isMinQuery != 0 )
          {
            sqlite3VdbeAddOp2( v, OP_Null, 0, regBase + nEq );
            nConstraint++;
            startEq = 0;
            start_constraints = 1;
          }
          codeApplyAffinity( pParse, regBase, nConstraint, zStartAff.ToString() );
          op = aStartOp[( start_constraints << 2 ) + ( startEq << 1 ) + bRev];
          Debug.Assert( op != 0 );
          testcase( op == OP_Rewind );
          testcase( op == OP_Last );
          testcase( op == OP_SeekGt );
          testcase( op == OP_SeekGe );
          testcase( op == OP_SeekLe );
          testcase( op == OP_SeekLt );
          sqlite3VdbeAddOp4Int( v, op, iIdxCur, addrNxt, regBase, nConstraint );

          /* Load the value for the inequality constraint at the end of the
          ** range (if any).
          */
          nConstraint = nEq;
          if ( pRangeEnd != null )
          {
            Expr pRight = pRangeEnd.pExpr.pRight;
            sqlite3ExprCacheRemove( pParse, regBase + nEq, 1 );
            sqlite3ExprCode( pParse, pRight, regBase + nEq );
            if ( ( pRangeEnd.wtFlags & TERM_VNULL ) == 0 )
            {
              sqlite3ExprCodeIsNullJump( v, pRight, regBase + nEq, addrNxt );
            }
            if ( zEndAff.Length > 0 )
            {
              if ( sqlite3CompareAffinity( pRight, zEndAff[nEq] ) == SQLITE_AFF_NONE )
              {
                /* Since the comparison is to be performed with no conversions
                ** applied to the operands, set the affinity to apply to pRight to 
                ** SQLITE_AFF_NONE.  */
                zEndAff[nEq] = SQLITE_AFF_NONE;
              }
              if ( ( sqlite3ExprNeedsNoAffinityChange( pRight, zEndAff[nEq] ) ) != 0 )
              {
                zEndAff[nEq] = SQLITE_AFF_NONE;
              }
            }
            codeApplyAffinity( pParse, regBase, nEq + 1, zEndAff.ToString() );
            nConstraint++;
            testcase( pRangeEnd.wtFlags & TERM_VIRTUAL ); /* EV: R-30575-11662 */
          }
          sqlite3DbFree( pParse.db, ref zStartAff );
          sqlite3DbFree( pParse.db, ref zEndAff );

          /* Top of the loop body */
          pLevel.p2 = sqlite3VdbeCurrentAddr( v );

          /* Check if the index cursor is past the end of the range. */
          op = aEndOp[( ( pRangeEnd != null || nEq != 0 ) ? 1 : 0 ) * ( 1 + bRev )];
          testcase( op == OP_Noop );
          testcase( op == OP_IdxGE );
          testcase( op == OP_IdxLT );
          if ( op != OP_Noop )
          {
            sqlite3VdbeAddOp4Int( v, op, iIdxCur, addrNxt, regBase, nConstraint );
            sqlite3VdbeChangeP5( v, (u8)( endEq != bRev ? 1 : 0 ) );
          }

          /* If there are inequality constraints, check that the value
          ** of the table column that the inequality contrains is not NULL.
          ** If it is, jump to the next iteration of the loop.
          */
          r1 = sqlite3GetTempReg( pParse );
          testcase( pLevel.plan.wsFlags & WHERE_BTM_LIMIT );
          testcase( pLevel.plan.wsFlags & WHERE_TOP_LIMIT );
          if ( ( pLevel.plan.wsFlags & ( WHERE_BTM_LIMIT | WHERE_TOP_LIMIT ) ) != 0 )
          {
            sqlite3VdbeAddOp3( v, OP_Column, iIdxCur, nEq, r1 );
            sqlite3VdbeAddOp2( v, OP_IsNull, r1, addrCont );
          }
          sqlite3ReleaseTempReg( pParse, r1 );

          /* Seek the table cursor, if required */
          disableTerm( pLevel, pRangeStart );
          disableTerm( pLevel, pRangeEnd );
          if ( 0 == omitTable )
          {
            iRowidReg = iReleaseReg = sqlite3GetTempReg( pParse );
            sqlite3VdbeAddOp2( v, OP_IdxRowid, iIdxCur, iRowidReg );
            sqlite3ExprCacheStore( pParse, iCur, -1, iRowidReg );
            sqlite3VdbeAddOp2( v, OP_Seek, iCur, iRowidReg );  /* Deferred seek */
          }

          /* Record the instruction used to terminate the loop. Disable
          ** WHERE clause terms made redundant by the index range scan.
          */
          if ( ( pLevel.plan.wsFlags & WHERE_UNIQUE ) != 0 )
          {
            pLevel.op = OP_Noop;
          }
          else if ( bRev != 0 )
          {
            pLevel.op = OP_Prev;
          }
          else
          {
            pLevel.op = OP_Next;
          }
          pLevel.p1 = iIdxCur;
        }
        else

#if  !SQLITE_OMIT_OR_OPTIMIZATION
          if ( ( pLevel.plan.wsFlags & WHERE_MULTI_OR ) != 0 )
          {
            /* Case 4:  Two or more separately indexed terms connected by OR
            **
            ** Example:
            **
            **   CREATE TABLE t1(a,b,c,d);
            **   CREATE INDEX i1 ON t1(a);
            **   CREATE INDEX i2 ON t1(b);
            **   CREATE INDEX i3 ON t1(c);
            **
            **   SELECT * FROM t1 WHERE a=5 OR b=7 OR (c=11 AND d=13)
            **
            ** In the example, there are three indexed terms connected by OR.
            ** The top of the loop looks like this:
            **
            **          Null       1                # Zero the rowset in reg 1
            **
            ** Then, for each indexed term, the following. The arguments to
            ** RowSetTest are such that the rowid of the current row is inserted
            ** into the RowSet. If it is already present, control skips the
            ** Gosub opcode and jumps straight to the code generated by WhereEnd().
            **
            **        sqlite3WhereBegin(<term>)
            **          RowSetTest                  # Insert rowid into rowset
            **          Gosub      2 A
            **        sqlite3WhereEnd()
            **
            ** Following the above, code to terminate the loop. Label A, the target
            ** of the Gosub above, jumps to the instruction right after the Goto.
            **
            **          Null       1                # Zero the rowset in reg 1
            **          Goto       B                # The loop is finished.
            **
            **       A: <loop body>                 # Return data, whatever.
            **
            **          Return     2                # Jump back to the Gosub
            **
            **       B: <after the loop>
            **
            */
            WhereClause pOrWc;    /* The OR-clause broken out into subterms */
            SrcList pOrTab;       /* Shortened table list or OR-clause generation */

            int regReturn = ++pParse.nMem;            /* Register used with OP_Gosub */
            int regRowset = 0;                        /* Register for RowSet object */
            int regRowid = 0;                         /* Register holding rowid */
            int iLoopBody = sqlite3VdbeMakeLabel( v );/* Start of loop body */
            int iRetInit;                             /* Address of regReturn init */
            int untestedTerms = 0;                    /* Some terms not completely tested */
            int ii;
            pTerm = pLevel.plan.u.pTerm;
            Debug.Assert( pTerm != null );
            Debug.Assert( pTerm.eOperator == WO_OR );
            Debug.Assert( ( pTerm.wtFlags & TERM_ORINFO ) != 0 );
            pOrWc = pTerm.u.pOrInfo.wc;
            pLevel.op = OP_Return;
            pLevel.p1 = regReturn;

            /* Set up a new SrcList in pOrTab containing the table being scanned
            ** by this loop in the a[0] slot and all notReady tables in a[1..] slots.
            ** This becomes the SrcList in the recursive call to sqlite3WhereBegin().
            */
            if ( pWInfo.nLevel > 1 )
            {
              int nNotReady;                 /* The number of notReady tables */
              SrcList_item[] origSrc;         /* Original list of tables */
              nNotReady = pWInfo.nLevel - iLevel - 1;
              //sqlite3StackAllocRaw(pParse.db,
              //sizeof(*pOrTab)+ nNotReady*sizeof(pOrTab.a[0]));
              pOrTab = new SrcList();
              pOrTab.a = new SrcList_item[nNotReady + 1];
              //if( pOrTab==0 ) return notReady;
              pOrTab.nAlloc = (i16)( nNotReady + 1 );
              pOrTab.nSrc = pOrTab.nAlloc;
              pOrTab.a[0] = pTabItem;//memcpy(pOrTab.a, pTabItem, sizeof(*pTabItem));
              origSrc = pWInfo.pTabList.a;
              for ( k = 1; k <= nNotReady; k++ )
              {
                pOrTab.a[k] = origSrc[pWInfo.a[iLevel + k].iFrom];// memcpy(&pOrTab.a[k], &origSrc[pLevel[k].iFrom], sizeof(pOrTab.a[k]));
              }
            }
            else
            {
              pOrTab = pWInfo.pTabList;
            }

            /* Initialize the rowset register to contain NULL. An SQL NULL is
            ** equivalent to an empty rowset.
            **
            ** Also initialize regReturn to contain the address of the instruction
            ** immediately following the OP_Return at the bottom of the loop. This
            ** is required in a few obscure LEFT JOIN cases where control jumps
            ** over the top of the loop into the body of it. In this case the
            ** correct response for the end-of-loop code (the OP_Return) is to
            ** fall through to the next instruction, just as an OP_Next does if
            ** called on an uninitialized cursor.
            */
            if ( ( wctrlFlags & WHERE_DUPLICATES_OK ) == 0 )
            {
              regRowset = ++pParse.nMem;
              regRowid = ++pParse.nMem;
              sqlite3VdbeAddOp2( v, OP_Null, 0, regRowset );
            }
            iRetInit = sqlite3VdbeAddOp2( v, OP_Integer, 0, regReturn );

            for ( ii = 0; ii < pOrWc.nTerm; ii++ )
            {
              WhereTerm pOrTerm = pOrWc.a[ii];
              if ( pOrTerm.leftCursor == iCur || pOrTerm.eOperator == WO_AND )
              {
                WhereInfo pSubWInfo;          /* Info for single OR-term scan */

                /* Loop through table entries that match term pOrTerm. */
                ExprList elDummy = null;
                pSubWInfo = sqlite3WhereBegin( pParse, pOrTab, pOrTerm.pExpr, ref elDummy,
                    WHERE_OMIT_OPEN | WHERE_OMIT_CLOSE |
                    WHERE_FORCE_TABLE | WHERE_ONETABLE_ONLY );
                if ( pSubWInfo != null )
                {
                  explainOneScan(
                  pParse, pOrTab, pSubWInfo.a[0], iLevel, pLevel.iFrom, 0
                  );
                  if ( ( wctrlFlags & WHERE_DUPLICATES_OK ) == 0 )
                  {
                    int iSet = ( ( ii == pOrWc.nTerm - 1 ) ? -1 : ii );
                    int r;
                    r = sqlite3ExprCodeGetColumn( pParse, pTabItem.pTab, -1, iCur,
                    regRowid );
                    sqlite3VdbeAddOp4Int( v, OP_RowSetTest, regRowset,
                                   sqlite3VdbeCurrentAddr( v ) + 2, r, iSet );
                  }
                  sqlite3VdbeAddOp2( v, OP_Gosub, regReturn, iLoopBody );

                  /* The pSubWInfo.untestedTerms flag means that this OR term
                  ** contained one or more AND term from a notReady table.  The
                  ** terms from the notReady table could not be tested and will
                  ** need to be tested later.
                  */
                  if ( pSubWInfo.untestedTerms != 0 )
                    untestedTerms = 1;

                  /* Finish the loop through table entries that match term pOrTerm. */
                  sqlite3WhereEnd( pSubWInfo );
                }
              }
            }
            sqlite3VdbeChangeP1( v, iRetInit, sqlite3VdbeCurrentAddr( v ) );
            sqlite3VdbeAddOp2( v, OP_Goto, 0, pLevel.addrBrk );
            sqlite3VdbeResolveLabel( v, iLoopBody );

            if ( pWInfo.nLevel > 1 )
              sqlite3DbFree( pParse.db, ref pOrTab );//sqlite3DbFree(pParse.db, pOrTab)
            if ( 0 == untestedTerms )
              disableTerm( pLevel, pTerm );
          }
          else
#endif //* SQLITE_OMIT_OR_OPTIMIZATION */

          {
            /* Case 5:  There is no usable index.  We must do a complete
            **          scan of the entire table.
            */
            u8[] aStep = new u8[] { OP_Next, OP_Prev };
            u8[] aStart = new u8[] { OP_Rewind, OP_Last };
            Debug.Assert( bRev == 0 || bRev == 1 );
            Debug.Assert( omitTable == 0 );
            pLevel.op = aStep[bRev];
            pLevel.p1 = iCur;
            pLevel.p2 = 1 + sqlite3VdbeAddOp2( v, aStart[bRev], iCur, addrBrk );
            pLevel.p5 = SQLITE_STMTSTATUS_FULLSCAN_STEP;
          }
      notReady &= ~getMask( pWC.pMaskSet, iCur );

      /* Insert code to test every subexpression that can be completely
      ** computed using the current set of tables.
      **
      ** IMPLEMENTATION-OF: R-49525-50935 Terms that cannot be satisfied through
      ** the use of indices become tests that are evaluated against each row of
      ** the relevant input tables.
      */
      for ( j = pWC.nTerm; j > 0; j-- )//, pTerm++)
      {
        pTerm = pWC.a[pWC.nTerm - j];
        Expr pE;
        testcase( pTerm.wtFlags & TERM_VIRTUAL ); /* IMP: R-30575-11662 */
        testcase( pTerm.wtFlags & TERM_CODED );
        if ( ( pTerm.wtFlags & ( TERM_VIRTUAL | TERM_CODED ) ) != 0 )
          continue;
        if ( ( pTerm.prereqAll & notReady ) != 0 )
        {
          testcase( pWInfo.untestedTerms == 0
          && ( pWInfo.wctrlFlags & WHERE_ONETABLE_ONLY ) != 0 );
          pWInfo.untestedTerms = 1;
          continue;
        }
        pE = pTerm.pExpr;
        Debug.Assert( pE != null );
        if ( pLevel.iLeftJoin != 0 && !( ( pE.flags & EP_FromJoin ) == EP_FromJoin ) )// !ExprHasProperty(pE, EP_FromJoin) ){
        {
          continue;
        }
        sqlite3ExprIfFalse( pParse, pE, addrCont, SQLITE_JUMPIFNULL );
        pTerm.wtFlags |= TERM_CODED;
      }

      /* For a LEFT OUTER JOIN, generate code that will record the fact that
      ** at least one row of the right table has matched the left table.
      */
      if ( pLevel.iLeftJoin != 0 )
      {
        pLevel.addrFirst = sqlite3VdbeCurrentAddr( v );
        sqlite3VdbeAddOp2( v, OP_Integer, 1, pLevel.iLeftJoin );
#if SQLITE_DEBUG
        VdbeComment( v, "record LEFT JOIN hit" );
#endif
        sqlite3ExprCacheClear( pParse );
        for ( j = 0; j < pWC.nTerm; j++ )//, pTerm++)
        {
          pTerm = pWC.a[j];
          testcase( pTerm.wtFlags & TERM_VIRTUAL );  /* IMP: R-30575-11662 */
          testcase( pTerm.wtFlags & TERM_CODED );
          if ( ( pTerm.wtFlags & ( TERM_VIRTUAL | TERM_CODED ) ) != 0 )
            continue;
          if ( ( pTerm.prereqAll & notReady ) != 0 )
          {
            Debug.Assert( pWInfo.untestedTerms != 0 );
            continue;
          }
          Debug.Assert( pTerm.pExpr != null );
          sqlite3ExprIfFalse( pParse, pTerm.pExpr, addrCont, SQLITE_JUMPIFNULL );
          pTerm.wtFlags |= TERM_CODED;
        }
      }

      sqlite3ReleaseTempReg( pParse, iReleaseReg );
      return notReady;
    }

#if  (SQLITE_TEST)
    /*
** The following variable holds a text description of query plan generated
** by the most recent call to sqlite3WhereBegin().  Each call to WhereBegin
** overwrites the previous.  This information is used for testing and
** analysis only.
*/
#if !TCLSH
    //char sqlite3_query_plan[BMS*2*40];  /* Text of the join */
    static StringBuilder sqlite3_query_plan;
#else
    static tcl.lang.Var.SQLITE3_GETSET sqlite3_query_plan = new tcl.lang.Var.SQLITE3_GETSET( "sqlite3_query_plan" );
#endif
    static int nQPlan = 0;              /* Next free slow in _query_plan[] */

#endif //* SQLITE_TEST */


    /*
** Free a WhereInfo structure
*/
    static void whereInfoFree( sqlite3 db, WhereInfo pWInfo )
    {
      if ( ALWAYS( pWInfo != null ) )
      {
        int i;
        for ( i = 0; i < pWInfo.nLevel; i++ )
        {
          sqlite3_index_info pInfo = pWInfo.a[i] != null ? pWInfo.a[i].pIdxInfo : null;
          if ( pInfo != null )
          {
            /* Debug.Assert( pInfo.needToFreeIdxStr==0 || db.mallocFailed ); */
            if ( pInfo.needToFreeIdxStr != 0 )
            {
              //sqlite3_free( ref pInfo.idxStr );
            }
            sqlite3DbFree( db, ref pInfo );
          }
          if ( pWInfo.a[i] != null && ( pWInfo.a[i].plan.wsFlags & WHERE_TEMP_INDEX ) != 0 )
          {
            Index pIdx = pWInfo.a[i].plan.u.pIdx;
            if ( pIdx != null )
            {
              sqlite3DbFree( db, ref pIdx.zColAff );
              sqlite3DbFree( db, ref pIdx );
            }
          }
        }
        whereClauseClear( pWInfo.pWC );
        sqlite3DbFree( db, ref pWInfo );
      }
    }


    /*
    ** Generate the beginning of the loop used for WHERE clause processing.
    ** The return value is a pointer to an opaque structure that contains
    ** information needed to terminate the loop.  Later, the calling routine
    ** should invoke sqlite3WhereEnd() with the return value of this function
    ** in order to complete the WHERE clause processing.
    **
    ** If an error occurs, this routine returns NULL.
    **
    ** The basic idea is to do a nested loop, one loop for each table in
    ** the FROM clause of a select.  (INSERT and UPDATE statements are the
    ** same as a SELECT with only a single table in the FROM clause.)  For
    ** example, if the SQL is this:
    **
    **       SELECT * FROM t1, t2, t3 WHERE ...;
    **
    ** Then the code generated is conceptually like the following:
    **
    **      foreach row1 in t1 do       \    Code generated
    **        foreach row2 in t2 do      |-- by sqlite3WhereBegin()
    **          foreach row3 in t3 do   /
    **            ...
    **          end                     \    Code generated
    **        end                        |-- by sqlite3WhereEnd()
    **      end                         /
    **
    ** Note that the loops might not be nested in the order in which they
    ** appear in the FROM clause if a different order is better able to make
    ** use of indices.  Note also that when the IN operator appears in
    ** the WHERE clause, it might result in additional nested loops for
    ** scanning through all values on the right-hand side of the IN.
    **
    ** There are Btree cursors Debug.Associated with each table.  t1 uses cursor
    ** number pTabList.a[0].iCursor.  t2 uses the cursor pTabList.a[1].iCursor.
    ** And so forth.  This routine generates code to open those VDBE cursors
    ** and sqlite3WhereEnd() generates the code to close them.
    **
    ** The code that sqlite3WhereBegin() generates leaves the cursors named
    ** in pTabList pointing at their appropriate entries.  The [...] code
    ** can use OP_Column and OP_Rowid opcodes on these cursors to extract
    ** data from the various tables of the loop.
    **
    ** If the WHERE clause is empty, the foreach loops must each scan their
    ** entire tables.  Thus a three-way join is an O(N^3) operation.  But if
    ** the tables have indices and there are terms in the WHERE clause that
    ** refer to those indices, a complete table scan can be avoided and the
    ** code will run much faster.  Most of the work of this routine is checking
    ** to see if there are indices that can be used to speed up the loop.
    **
    ** Terms of the WHERE clause are also used to limit which rows actually
    ** make it to the "..." in the middle of the loop.  After each "foreach",
    ** terms of the WHERE clause that use only terms in that loop and outer
    ** loops are evaluated and if false a jump is made around all subsequent
    ** inner loops (or around the "..." if the test occurs within the inner-
    ** most loop)
    **
    ** OUTER JOINS
    **
    ** An outer join of tables t1 and t2 is conceptally coded as follows:
    **
    **    foreach row1 in t1 do
    **      flag = 0
    **      foreach row2 in t2 do
    **        start:
    **          ...
    **          flag = 1
    **      end
    **      if flag==null then
    **        move the row2 cursor to a null row
    **        goto start
    **      fi
    **    end
    **
    ** ORDER BY CLAUSE PROCESSING
    **
    ** ppOrderBy is a pointer to the ORDER BY clause of a SELECT statement,
    ** if there is one.  If there is no ORDER BY clause or if this routine
    ** is called from an UPDATE or DELETE statement, then ppOrderBy is NULL.
    **
    ** If an index can be used so that the natural output order of the table
    ** scan is correct for the ORDER BY clause, then that index is used and
    ** ppOrderBy is set to NULL.  This is an optimization that prevents an
    ** unnecessary sort of the result set if an index appropriate for the
    ** ORDER BY clause already exists.
    **
    ** If the where clause loops cannot be arranged to provide the correct
    ** output order, then the ppOrderBy is unchanged.
    */
    static WhereInfo sqlite3WhereBegin(
    Parse pParse,           /* The parser context */
    SrcList pTabList,       /* A list of all tables to be scanned */
    Expr pWhere,            /* The WHERE clause */
    ref ExprList ppOrderBy, /* An ORDER BY clause, or NULL */
    u16 wctrlFlags          /* One of the WHERE_* flags defined in sqliteInt.h */
    )
    {
      int i;                     /* Loop counter */
      int nByteWInfo;            /* Num. bytes allocated for WhereInfo struct */
      int nTabList;              /* Number of elements in pTabList */
      WhereInfo pWInfo;          /* Will become the return value of this function */
      Vdbe v = pParse.pVdbe;     /* The virtual data_base engine */
      Bitmask notReady;          /* Cursors that are not yet positioned */
      WhereMaskSet pMaskSet;     /* The expression mask set */
      WhereClause pWC = new WhereClause();               /* Decomposition of the WHERE clause */
      SrcList_item pTabItem;     /* A single entry from pTabList */
      WhereLevel pLevel;         /* A single level in the pWInfo list */
      int iFrom;                 /* First unused FROM clause element */
      int andFlags;              /* AND-ed combination of all pWC.a[].wtFlags */
      sqlite3 db;                /* Data_base connection */

      /* The number of tables in the FROM clause is limited by the number of
      ** bits in a Bitmask
      */
      testcase( pTabList.nSrc == BMS );
      if ( pTabList.nSrc > BMS )
      {
        sqlite3ErrorMsg( pParse, "at most %d tables in a join", BMS );
        return null;
      }

      /* This function normally generates a nested loop for all tables in 
      ** pTabList.  But if the WHERE_ONETABLE_ONLY flag is set, then we should
      ** only generate code for the first table in pTabList and assume that
      ** any cursors associated with subsequent tables are uninitialized.
      */
      nTabList = ( ( wctrlFlags & WHERE_ONETABLE_ONLY ) != 0 ) ? 1 : (int)pTabList.nSrc;

      /* Allocate and initialize the WhereInfo structure that will become the
      ** return value. A single allocation is used to store the WhereInfo
      ** struct, the contents of WhereInfo.a[], the WhereClause structure
      ** and the WhereMaskSet structure. Since WhereClause contains an 8-byte
      ** field (type Bitmask) it must be aligned on an 8-byte boundary on
      ** some architectures. Hence the ROUND8() below.
      */
      db = pParse.db;
      pWInfo = new WhereInfo();
      //nByteWInfo = ROUND8(sizeof(WhereInfo)+(nTabList-1)*sizeof(WhereLevel));
      //pWInfo = sqlite3DbMallocZero( db,
      //    nByteWInfo +
      //    sizeof( WhereClause ) +
      //    sizeof( WhereMaskSet )
      //);
      pWInfo.a = new WhereLevel[pTabList.nSrc];
      for ( int ai = 0; ai < pWInfo.a.Length; ai++ )
      {
        pWInfo.a[ai] = new WhereLevel();
      }
      //if ( db.mallocFailed != 0 )
      //{
      //sqlite3DbFree(db, pWInfo);
      //pWInfo = 0;
      //  goto whereBeginError;
      //}
      pWInfo.nLevel = nTabList;
      pWInfo.pParse = pParse;
      pWInfo.pTabList = pTabList;
      pWInfo.iBreak = sqlite3VdbeMakeLabel( v );
      pWInfo.pWC = pWC = new WhereClause();// (WhereClause )((u8 )pWInfo)[nByteWInfo];
      pWInfo.wctrlFlags = wctrlFlags;
      pWInfo.savedNQueryLoop = pParse.nQueryLoop;
      //pMaskSet = (WhereMaskSet)pWC[1];

      /* Split the WHERE clause into separate subexpressions where each
      ** subexpression is separated by an AND operator.
      */
      pMaskSet = new WhereMaskSet();//initMaskSet(pMaskSet);
      whereClauseInit( pWC, pParse, pMaskSet );
      sqlite3ExprCodeConstants( pParse, pWhere );
      whereSplit( pWC, pWhere, TK_AND );   /* IMP: R-15842-53296 */

      /* Special case: a WHERE clause that is constant.  Evaluate the
      ** expression and either jump over all of the code or fall thru.
      */
      if ( pWhere != null && ( nTabList == 0 || sqlite3ExprIsConstantNotJoin( pWhere ) != 0 ) )
      {
        sqlite3ExprIfFalse( pParse, pWhere, pWInfo.iBreak, SQLITE_JUMPIFNULL );
        pWhere = null;
      }

      /* Assign a bit from the bitmask to every term in the FROM clause.
      **
      ** When assigning bitmask values to FROM clause cursors, it must be
      ** the case that if X is the bitmask for the N-th FROM clause term then
      ** the bitmask for all FROM clause terms to the left of the N-th term
      ** is (X-1).   An expression from the ON clause of a LEFT JOIN can use
      ** its Expr.iRightJoinTable value to find the bitmask of the right table
      ** of the join.  Subtracting one from the right table bitmask gives a
      ** bitmask for all tables to the left of the join.  Knowing the bitmask
      ** for all tables to the left of a left join is important.  Ticket #3015.
      **
      ** Configure the WhereClause.vmask variable so that bits that correspond
      ** to virtual table cursors are set. This is used to selectively disable
      ** the OR-to-IN transformation in exprAnalyzeOrTerm(). It is not helpful
      ** with virtual tables.
      **
      ** Note that bitmasks are created for all pTabList.nSrc tables in
      ** pTabList, not just the first nTabList tables.  nTabList is normally
      ** equal to pTabList.nSrc but might be shortened to 1 if the
      ** WHERE_ONETABLE_ONLY flag is set.
      */
      Debug.Assert( pWC.vmask == 0 && pMaskSet.n == 0 );
      for ( i = 0; i < pTabList.nSrc; i++ )
      {
        createMask( pMaskSet, pTabList.a[i].iCursor );
#if !SQLITE_OMIT_VIRTUALTABLE
        if ( ALWAYS( pTabList.a[i].pTab ) && IsVirtual( pTabList.a[i].pTab ) )
        {
          pWC.vmask |= ( (Bitmask)1 << i );
        }
#endif
      }
#if  !NDEBUG
      {
        Bitmask toTheLeft = 0;
        for ( i = 0; i < pTabList.nSrc; i++ )
        {
          Bitmask m = getMask( pMaskSet, pTabList.a[i].iCursor );
          Debug.Assert( ( m - 1 ) == toTheLeft );
          toTheLeft |= m;
        }
      }
#endif

      /* Analyze all of the subexpressions.  Note that exprAnalyze() might
** add new virtual terms onto the end of the WHERE clause.  We do not
** want to analyze these virtual terms, so start analyzing at the end
** and work forward so that the added virtual terms are never processed.
*/
      exprAnalyzeAll( pTabList, pWC );
      //if ( db.mallocFailed != 0 )
      //{
      //  goto whereBeginError;
      //}

      /* Chose the best index to use for each table in the FROM clause.
      **
      ** This loop fills in the following fields:
      **
      **   pWInfo.a[].pIdx      The index to use for this level of the loop.
      **   pWInfo.a[].wsFlags   WHERE_xxx flags Debug.Associated with pIdx
      **   pWInfo.a[].nEq       The number of == and IN constraints
      **   pWInfo.a[].iFrom     Which term of the FROM clause is being coded
      **   pWInfo.a[].iTabCur   The VDBE cursor for the data_base table
      **   pWInfo.a[].iIdxCur   The VDBE cursor for the index
      **   pWInfo.a[].pTerm     When wsFlags==WO_OR, the OR-clause term
      **
      ** This loop also figures out the nesting order of tables in the FROM
      ** clause.
      */
      notReady = ~(Bitmask)0;
      andFlags = ~0;
#if (SQLITE_TEST) && (SQLITE_DEBUG)
      WHERETRACE( "*** Optimizer Start ***\n" );
#endif
      for ( i = iFrom = 0; i < nTabList; i++ )//, pLevel++ )
      {
        pLevel = pWInfo.a[i];
        WhereCost bestPlan;         /* Most efficient plan seen so far */
        Index pIdx;                 /* Index for FROM table at pTabItem */
        int j;                      /* For looping over FROM tables */
        int bestJ = -1;             /* The value of j */
        Bitmask m;                  /* Bitmask value for j or bestJ */
        int isOptimal;              /* Iterator for optimal/non-optimal search */
        int nUnconstrained;         /* Number tables without INDEXED BY */
        Bitmask notIndexed;         /* Mask of tables that cannot use an index */

        bestPlan = new WhereCost();// memset( &bestPlan, 0, sizeof( bestPlan ) );
        bestPlan.rCost = SQLITE_BIG_DBL;
#if  (SQLITE_TEST) && (SQLITE_DEBUG)
        WHERETRACE( "*** Begin search for loop %d ***\n", i );
#endif

        /* Loop through the remaining entries in the FROM clause to find the
** next nested loop. The loop tests all FROM clause entries
** either once or twice. 
**
** The first test is always performed if there are two or more entries
** remaining and never performed if there is only one FROM clause entry
** to choose from.  The first test looks for an "optimal" scan.  In
** this context an optimal scan is one that uses the same strategy
** for the given FROM clause entry as would be selected if the entry
** were used as the innermost nested loop.  In other words, a table
** is chosen such that the cost of running that table cannot be reduced
** by waiting for other tables to run first.  This "optimal" test works
** by first assuming that the FROM clause is on the inner loop and finding
** its query plan, then checking to see if that query plan uses any
** other FROM clause terms that are notReady.  If no notReady terms are
** used then the "optimal" query plan works.
**
** Note that the WhereCost.nRow parameter for an optimal scan might
** not be as small as it would be if the table really were the innermost
** join.  The nRow value can be reduced by WHERE clause constraints
** that do not use indices.  But this nRow reduction only happens if the
** table really is the innermost join.  
**
** The second loop iteration is only performed if no optimal scan
** strategies were found by the first iteration. This second iteration
** is used to search for the lowest cost scan overall.
**
** Previous versions of SQLite performed only the second iteration -
** the next outermost loop was always that with the lowest overall
** cost. However, this meant that SQLite could select the wrong plan
** for scripts such as the following:
**   
**   CREATE TABLE t1(a, b); 
**   CREATE TABLE t2(c, d);
**   SELECT * FROM t2, t1 WHERE t2.rowid = t1.a;
**
** The best strategy is to iterate through table t1 first. However it
** is not possible to determine this with a simple greedy algorithm.
** Since the cost of a linear scan through table t2 is the same 
** as the cost of a linear scan through table t1, a simple greedy 
** algorithm may choose to use t2 for the outer loop, which is a much
** costlier approach.
*/
        nUnconstrained = 0;
        notIndexed = 0;
        for ( isOptimal = ( iFrom < nTabList - 1 ) ? 1 : 0; isOptimal >= 0 && bestJ < 0; isOptimal-- )
        {
          Bitmask mask;  /* Mask of tables not yet ready */
          for ( j = iFrom; j < nTabList; j++ )//, pTabItem++)
          {
            pTabItem = pTabList.a[j];
            int doNotReorder;       /* True if this table should not be reordered */
            WhereCost sCost = new WhereCost(); /* Cost information from best[Virtual]Index() */
            ExprList pOrderBy;      /* ORDER BY clause for index to optimize */

            doNotReorder = ( pTabItem.jointype & ( JT_LEFT | JT_CROSS ) ) != 0 ? 1 : 0;
            if ( ( j != iFrom && doNotReorder != 0 ) )
              break;
            m = getMask( pMaskSet, pTabItem.iCursor );
            if ( ( m & notReady ) == 0 )
            {
              if ( j == iFrom )
                iFrom++;
              continue;
            }
            mask = ( isOptimal != 0 ? m : notReady );
            pOrderBy = ( ( i == 0 && ppOrderBy != null ) ? ppOrderBy : null );
            if ( pTabItem.pIndex == null )
              nUnconstrained++;

#if  (SQLITE_TEST) && (SQLITE_DEBUG)
            WHERETRACE( "=== trying table %d with isOptimal=%d ===\n",
            j, isOptimal );
#endif
            Debug.Assert( pTabItem.pTab != null );
#if  !SQLITE_OMIT_VIRTUALTABLE
            if ( IsVirtual( pTabItem.pTab ) )
            {
              sqlite3_index_info pp = pWInfo.a[j].pIdxInfo;
              bestVirtualIndex( pParse, pWC, pTabItem, mask, notReady, pOrderBy,
               ref sCost, ref pp );
            }
            else
#endif
            {
              bestBtreeIndex( pParse, pWC, pTabItem, mask, notReady, pOrderBy,
              ref sCost );
            }
            Debug.Assert( isOptimal != 0 || ( sCost.used & notReady ) == 0 );

            /* If an INDEXED BY clause is present, then the plan must use that
            ** index if it uses any index at all */
            Debug.Assert( pTabItem.pIndex == null
            || ( sCost.plan.wsFlags & WHERE_NOT_FULLSCAN ) == 0
            || sCost.plan.u.pIdx == pTabItem.pIndex );

            if ( isOptimal != 0 && ( sCost.plan.wsFlags & WHERE_NOT_FULLSCAN ) == 0 )
            {
              notIndexed |= m;
            }

            /* Conditions under which this table becomes the best so far:
            **
            **   (1) The table must not depend on other tables that have not
            **       yet run.
            **
            **   (2) A full-table-scan plan cannot supercede indexed plan unless
            **       the full-table-scan is an "optimal" plan as defined above.
            **
            **   (3) All tables have an INDEXED BY clause or this table lacks an
            **       INDEXED BY clause or this table uses the specific
            **       index specified by its INDEXED BY clause.  This rule ensures
            **       that a best-so-far is always selected even if an impossible
            **       combination of INDEXED BY clauses are given.  The error
            **       will be detected and relayed back to the application later.
            **       The NEVER() comes about because rule (2) above prevents
            **       An indexable full-table-scan from reaching rule (3).
            **
            **   (4) The plan cost must be lower than prior plans or else the
            **       cost must be the same and the number of rows must be lower.
            */
            if ( ( sCost.used & notReady ) == 0                       /* (1) */
                && ( bestJ < 0 || ( notIndexed & m ) != 0               /* (2) */
                    || ( bestPlan.plan.wsFlags & WHERE_NOT_FULLSCAN ) == 0
                    || ( sCost.plan.wsFlags & WHERE_NOT_FULLSCAN ) != 0 )
                && ( nUnconstrained == 0 || pTabItem.pIndex == null   /* (3) */
                || NEVER( ( sCost.plan.wsFlags & WHERE_NOT_FULLSCAN ) != 0 ) )
            && ( bestJ < 0 || sCost.rCost < bestPlan.rCost          /* (4) */
            || ( sCost.rCost <= bestPlan.rCost
            && sCost.plan.nRow < bestPlan.plan.nRow ) )
            )
            {
#if  (SQLITE_TEST) && (SQLITE_DEBUG)
              WHERETRACE( "=== table %d is best so far" +
              " with cost=%g and nRow=%g\n",
              j, sCost.rCost, sCost.plan.nRow );
#endif
              bestPlan = sCost;
              bestJ = j;
            }
            if ( doNotReorder != 0 )
              break;
          }
        }
        Debug.Assert( bestJ >= 0 );
        Debug.Assert( ( notReady & getMask( pMaskSet, pTabList.a[bestJ].iCursor ) ) != 0 );
#if (SQLITE_TEST) && (SQLITE_DEBUG)
        WHERETRACE( "*** Optimizer selects table %d for loop %d" +
        " with cost=%g and nRow=%g\n",
        bestJ, i,//pLevel-pWInfo.a,
        bestPlan.rCost, bestPlan.plan.nRow );
#endif
        if ( ( bestPlan.plan.wsFlags & WHERE_ORDERBY ) != 0 )
        {
          ppOrderBy = null;
        }
        andFlags = (int)( andFlags & bestPlan.plan.wsFlags );
        pLevel.plan = bestPlan.plan;
        testcase( bestPlan.plan.wsFlags & WHERE_INDEXED );
        testcase( bestPlan.plan.wsFlags & WHERE_TEMP_INDEX );
        if ( ( bestPlan.plan.wsFlags & ( WHERE_INDEXED | WHERE_TEMP_INDEX ) ) != 0 )
        {
          pLevel.iIdxCur = pParse.nTab++;
        }
        else
        {
          pLevel.iIdxCur = -1;
        }
        notReady &= ~getMask( pMaskSet, pTabList.a[bestJ].iCursor );
        pLevel.iFrom = (u8)bestJ;
        if ( bestPlan.plan.nRow >= (double)1 )
        {
          pParse.nQueryLoop *= bestPlan.plan.nRow;
        }

        /* Check that if the table scanned by this loop iteration had an
        ** INDEXED BY clause attached to it, that the named index is being
        ** used for the scan. If not, then query compilation has failed.
        ** Return an error.
        */
        pIdx = pTabList.a[bestJ].pIndex;
        if ( pIdx != null )
        {
          if ( ( bestPlan.plan.wsFlags & WHERE_INDEXED ) == 0 )
          {
            sqlite3ErrorMsg( pParse, "cannot use index: %s", pIdx.zName );
            goto whereBeginError;
          }
          else
          {
            /* If an INDEXED BY clause is used, the bestIndex() function is
            ** guaranteed to find the index specified in the INDEXED BY clause
            ** if it find an index at all. */
            Debug.Assert( bestPlan.plan.u.pIdx == pIdx );
          }
        }
      }
#if (SQLITE_TEST) && (SQLITE_DEBUG)
      WHERETRACE( "*** Optimizer Finished ***\n" );
#endif
      if ( pParse.nErr != 0 /*|| db.mallocFailed != 0 */ )
      {
        goto whereBeginError;
      }

      /* If the total query only selects a single row, then the ORDER BY
      ** clause is irrelevant.
      */
      if ( ( andFlags & WHERE_UNIQUE ) != 0 && ppOrderBy != null )
      {
        ppOrderBy = null;
      }

      /* If the caller is an UPDATE or DELETE statement that is requesting
      ** to use a one-pDebug.Ass algorithm, determine if this is appropriate.
      ** The one-pass algorithm only works if the WHERE clause constraints
      ** the statement to update a single row.
      */
      Debug.Assert( ( wctrlFlags & WHERE_ONEPASS_DESIRED ) == 0 || pWInfo.nLevel == 1 );
      if ( ( wctrlFlags & WHERE_ONEPASS_DESIRED ) != 0 && ( andFlags & WHERE_UNIQUE ) != 0 )
      {
        pWInfo.okOnePass = 1;
        pWInfo.a[0].plan.wsFlags = (u32)( pWInfo.a[0].plan.wsFlags & ~WHERE_IDX_ONLY );
      }

      /* Open all tables in the pTabList and any indices selected for
      ** searching those tables.
      */
      sqlite3CodeVerifySchema( pParse, -1 ); /* Insert the cookie verifier Goto */
      notReady = ~(Bitmask)0;
      pWInfo.nRowOut = (double)1;
      for ( i = 0; i < nTabList; i++ )//, pLevel++ )
      {
        pLevel = pWInfo.a[i];
        Table pTab;     /* Table to open */
        int iDb;         /* Index of data_base containing table/index */

        pTabItem = pTabList.a[pLevel.iFrom];
        pTab = pTabItem.pTab;
        pLevel.iTabCur = pTabItem.iCursor;
        pWInfo.nRowOut *= pLevel.plan.nRow;
        iDb = sqlite3SchemaToIndex( db, pTab.pSchema );
        if ( ( pTab.tabFlags & TF_Ephemeral ) != 0 || pTab.pSelect != null )
        {
          /* Do nothing */
        }
        else
#if  !SQLITE_OMIT_VIRTUALTABLE
          if ( ( pLevel.plan.wsFlags & WHERE_VIRTUALTABLE ) != 0 )
          {
            VTable pVTab = sqlite3GetVTable( db, pTab );
            int iCur = pTabItem.iCursor;
            sqlite3VdbeAddOp4( v, OP_VOpen, iCur, 0, 0,
            pVTab, P4_VTAB );
          }
          else
#endif
            if ( ( pLevel.plan.wsFlags & WHERE_IDX_ONLY ) == 0
            && ( wctrlFlags & WHERE_OMIT_OPEN ) == 0 )
            {
              int op = pWInfo.okOnePass != 0 ? OP_OpenWrite : OP_OpenRead;
              sqlite3OpenTable( pParse, pTabItem.iCursor, iDb, pTab, op );
              testcase( pTab.nCol == BMS - 1 );
              testcase( pTab.nCol == BMS );
              if ( 0 == pWInfo.okOnePass && pTab.nCol < BMS )
              {
                Bitmask b = pTabItem.colUsed;
                int n = 0;
                for ( ; b != 0; b = b >> 1, n++ )
                {
                }
                sqlite3VdbeChangeP4( v, sqlite3VdbeCurrentAddr( v ) - 1,
                        n, P4_INT32 );//SQLITE_INT_TO_PTR(n)
                Debug.Assert( n <= pTab.nCol );
              }
            }
            else
            {
              sqlite3TableLock( pParse, iDb, pTab.tnum, 0, pTab.zName );
            }
#if !SQLITE_OMIT_AUTOMATIC_INDEX
        if ( ( pLevel.plan.wsFlags & WHERE_TEMP_INDEX ) != 0 )
        {
          constructAutomaticIndex( pParse, pWC, pTabItem, notReady, pLevel );
        }
        else
#endif
          if ( ( pLevel.plan.wsFlags & WHERE_INDEXED ) != 0 )
          {
            Index pIx = pLevel.plan.u.pIdx;
            KeyInfo pKey = sqlite3IndexKeyinfo( pParse, pIx );
            int iIdxCur = pLevel.iIdxCur;
            Debug.Assert( pIx.pSchema == pTab.pSchema );
            Debug.Assert( iIdxCur >= 0 );
            sqlite3VdbeAddOp4( v, OP_OpenRead, iIdxCur, pIx.tnum, iDb,
            pKey, P4_KEYINFO_HANDOFF );
#if SQLITE_DEBUG
            VdbeComment( v, "%s", pIx.zName );
#endif
          }
        sqlite3CodeVerifySchema( pParse, iDb );
        notReady &= ~getMask( pWC.pMaskSet, pTabItem.iCursor );
      }
      pWInfo.iTop = sqlite3VdbeCurrentAddr( v );
      //if( db.mallocFailed ) goto whereBeginError;

      /* Generate the code to do the search.  Each iteration of the for
      ** loop below generates code for a single nested loop of the VM
      ** program.
      */
      notReady = ~(Bitmask)0;
      for ( i = 0; i < nTabList; i++ )
      {
        pLevel = pWInfo.a[i];
        explainOneScan( pParse, pTabList, pLevel, i, pLevel.iFrom, wctrlFlags );
        notReady = codeOneLoopStart( pWInfo, i, wctrlFlags, notReady );
        pWInfo.iContinue = pLevel.addrCont;
      }

#if SQLITE_TEST  //* For testing and debugging use only */
      /* Record in the query plan information about the current table
** and the index used to access it (if any).  If the table itself
** is not used, its name is just '{}'.  If no index is used
** the index is listed as "{}".  If the primary key is used the
** index name is '*'.
*/
#if !TCLSH
      sqlite3_query_plan.Length = 0;
#else
      sqlite3_query_plan.sValue = string.Empty;
#endif
      for ( i = 0; i < nTabList; i++ )
      {
        string z;
        int n;
        pLevel = pWInfo.a[i];
        pTabItem = pTabList.a[pLevel.iFrom];
        z = pTabItem.zAlias;
        if ( z == null )
          z = pTabItem.pTab.zName;
        n = sqlite3Strlen30( z );
        if ( true ) //n+nQPlan < sizeof(sqlite3_query_plan)-10 )
        {
          if ( ( pLevel.plan.wsFlags & WHERE_IDX_ONLY ) != 0 )
          {
            sqlite3_query_plan.Append( "{}" ); //memcpy( &sqlite3_query_plan[nQPlan], "{}", 2 );
            nQPlan += 2;
          }
          else
          {
            sqlite3_query_plan.Append( z ); //memcpy( &sqlite3_query_plan[nQPlan], z, n );
            nQPlan += n;
          }
          sqlite3_query_plan.Append( " " );
          nQPlan++; //sqlite3_query_plan[nQPlan++] = ' ';
        }
        testcase( pLevel.plan.wsFlags & WHERE_ROWID_EQ );
        testcase( pLevel.plan.wsFlags & WHERE_ROWID_RANGE );
        if ( ( pLevel.plan.wsFlags & ( WHERE_ROWID_EQ | WHERE_ROWID_RANGE ) ) != 0 )
        {
          sqlite3_query_plan.Append( "* " ); //memcpy(&sqlite3_query_plan[nQPlan], "* ", 2);
          nQPlan += 2;
        }
        else if ( ( pLevel.plan.wsFlags & WHERE_INDEXED ) != 0 )
        {
          n = sqlite3Strlen30( pLevel.plan.u.pIdx.zName );
          if ( true ) //n+nQPlan < sizeof(sqlite3_query_plan)-2 )//if( n+nQPlan < sizeof(sqlite3_query_plan)-2 )
          {
            sqlite3_query_plan.Append( pLevel.plan.u.pIdx.zName ); //memcpy(&sqlite3_query_plan[nQPlan], pLevel.plan.u.pIdx.zName, n);
            nQPlan += n;
            sqlite3_query_plan.Append( " " ); //sqlite3_query_plan[nQPlan++] = ' ';
          }
        }
        else
        {
          sqlite3_query_plan.Append( "{} " ); //memcpy( &sqlite3_query_plan[nQPlan], "{} ", 3 );
          nQPlan += 3;
        }
      }
      //while( nQPlan>0 && sqlite3_query_plan[nQPlan-1]==' ' ){
      //  sqlite3_query_plan[--nQPlan] = 0;
      //}
      //sqlite3_query_plan[nQPlan] = 0;
#if !TCLSH
      sqlite3_query_plan = new StringBuilder( sqlite3_query_plan.ToString().Trim() );
#else
      sqlite3_query_plan.Trim();
#endif
      nQPlan = 0;
#endif //* SQLITE_TEST // Testing and debugging use only */

      /* Record the continuation address in the WhereInfo structure.  Then
** clean up and return.
*/
      return pWInfo;

    /* Jump here if malloc fails */
whereBeginError:
      if ( pWInfo != null )
      {
        pParse.nQueryLoop = pWInfo.savedNQueryLoop;
        whereInfoFree( db, pWInfo );
      }
      return null;
    }

    /*
    ** Generate the end of the WHERE loop.  See comments on
    ** sqlite3WhereBegin() for additional information.
    */
    static void sqlite3WhereEnd( WhereInfo pWInfo )
    {
      Parse pParse = pWInfo.pParse;
      Vdbe v = pParse.pVdbe;
      int i;
      WhereLevel pLevel;
      SrcList pTabList = pWInfo.pTabList;
      sqlite3 db = pParse.db;

      /* Generate loop termination code.
      */
      sqlite3ExprCacheClear( pParse );
      for ( i = pWInfo.nLevel - 1; i >= 0; i-- )
      {
        pLevel = pWInfo.a[i];
        sqlite3VdbeResolveLabel( v, pLevel.addrCont );
        if ( pLevel.op != OP_Noop )
        {
          sqlite3VdbeAddOp2( v, pLevel.op, pLevel.p1, pLevel.p2 );
          sqlite3VdbeChangeP5( v, pLevel.p5 );
        }
        if ( ( pLevel.plan.wsFlags & WHERE_IN_ABLE ) != 0 && pLevel.u._in.nIn > 0 )
        {
          InLoop pIn;
          int j;
          sqlite3VdbeResolveLabel( v, pLevel.addrNxt );
          for ( j = pLevel.u._in.nIn; j > 0; j-- )//, pIn--)
          {
            pIn = pLevel.u._in.aInLoop[j - 1];
            sqlite3VdbeJumpHere( v, pIn.addrInTop + 1 );
            sqlite3VdbeAddOp2( v, OP_Next, pIn.iCur, pIn.addrInTop );
            sqlite3VdbeJumpHere( v, pIn.addrInTop - 1 );
          }
          sqlite3DbFree( db, ref pLevel.u._in.aInLoop );
        }
        sqlite3VdbeResolveLabel( v, pLevel.addrBrk );
        if ( pLevel.iLeftJoin != 0 )
        {
          int addr;
          addr = sqlite3VdbeAddOp1( v, OP_IfPos, pLevel.iLeftJoin );
          Debug.Assert( ( pLevel.plan.wsFlags & WHERE_IDX_ONLY ) == 0
          || ( pLevel.plan.wsFlags & WHERE_INDEXED ) != 0 );
          if ( ( pLevel.plan.wsFlags & WHERE_IDX_ONLY ) == 0 )
          {
            sqlite3VdbeAddOp1( v, OP_NullRow, pTabList.a[i].iCursor );
          }
          if ( pLevel.iIdxCur >= 0 )
          {
            sqlite3VdbeAddOp1( v, OP_NullRow, pLevel.iIdxCur );
          }
          if ( pLevel.op == OP_Return )
          {
            sqlite3VdbeAddOp2( v, OP_Gosub, pLevel.p1, pLevel.addrFirst );
          }
          else
          {
            sqlite3VdbeAddOp2( v, OP_Goto, 0, pLevel.addrFirst );
          }
          sqlite3VdbeJumpHere( v, addr );
        }
      }

      /* The "break" point is here, just past the end of the outer loop.
      ** Set it.
      */
      sqlite3VdbeResolveLabel( v, pWInfo.iBreak );

      /* Close all of the cursors that were opened by sqlite3WhereBegin.
      */
      Debug.Assert( pWInfo.nLevel == 1 || pWInfo.nLevel == pTabList.nSrc );
      for ( i = 0; i < pWInfo.nLevel; i++ )//  for(i=0, pLevel=pWInfo.a; i<pWInfo.nLevel; i++, pLevel++){
      {
        pLevel = pWInfo.a[i];
        SrcList_item pTabItem = pTabList.a[pLevel.iFrom];
        Table pTab = pTabItem.pTab;
        Debug.Assert( pTab != null );
        if ( ( pTab.tabFlags & TF_Ephemeral ) == 0
        && pTab.pSelect == null
        && ( pWInfo.wctrlFlags & WHERE_OMIT_CLOSE ) == 0
        )
        {
          u32 ws = pLevel.plan.wsFlags;
          if ( 0 == pWInfo.okOnePass && ( ws & WHERE_IDX_ONLY ) == 0 )
          {
            sqlite3VdbeAddOp1( v, OP_Close, pTabItem.iCursor );
          }
          if ( ( ws & WHERE_INDEXED ) != 0 && ( ws & WHERE_TEMP_INDEX ) == 0 )
          {
            sqlite3VdbeAddOp1( v, OP_Close, pLevel.iIdxCur );
          }
        }

        /* If this scan uses an index, make code substitutions to read data
        ** from the index in preference to the table. Sometimes, this means
        ** the table need never be read from. This is a performance boost,
        ** as the vdbe level waits until the table is read before actually
        ** seeking the table cursor to the record corresponding to the current
        ** position in the index.
        **
        ** Calls to the code generator in between sqlite3WhereBegin and
        ** sqlite3WhereEnd will have created code that references the table
        ** directly.  This loop scans all that code looking for opcodes
        ** that reference the table and converts them into opcodes that
        ** reference the index.
        */
        if ( ( pLevel.plan.wsFlags & WHERE_INDEXED ) != 0 )///* && 0 == db.mallocFailed */ )
        {
          int k, j, last;
          VdbeOp pOp;
          Index pIdx = pLevel.plan.u.pIdx;

          Debug.Assert( pIdx != null );
          //pOp = sqlite3VdbeGetOp( v, pWInfo.iTop );
          last = sqlite3VdbeCurrentAddr( v );
          for ( k = pWInfo.iTop; k < last; k++ )//, pOp++ )
          {
            pOp = sqlite3VdbeGetOp( v, k );
            if ( pOp.p1 != pLevel.iTabCur )
              continue;
            if ( pOp.opcode == OP_Column )
            {
              for ( j = 0; j < pIdx.nColumn; j++ )
              {
                if ( pOp.p2 == pIdx.aiColumn[j] )
                {
                  pOp.p2 = j;
                  pOp.p1 = pLevel.iIdxCur;
                  break;
                }
              }
              Debug.Assert( ( pLevel.plan.wsFlags & WHERE_IDX_ONLY ) == 0
              || j < pIdx.nColumn );

            }
            else if ( pOp.opcode == OP_Rowid )
            {
              pOp.p1 = pLevel.iIdxCur;
              pOp.opcode = OP_IdxRowid;
            }
          }
        }
      }

      /* Final cleanup
      */
      pParse.nQueryLoop = pWInfo.savedNQueryLoop;
      whereInfoFree( db, pWInfo );
      return;
    }
  }
}