**    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.
**
*************************************************************************
** Internal interface definitions for SQLite.
**
** @(#) $Id: sqliteInt.h,v 1.149 2002/11/20 11:55:19 drh Exp $
*/
#include "config.h"
#include "sqlite.h"
#include "hash.h"
#include "vdbe.h"
#include "parse.h"
#include "btree.h"
................................................................................
  int score;           /* How well this indexed scored */
  int brk;             /* Jump here to break out of the loop */
  int cont;            /* Jump here to continue with the next loop cycle */
  int op, p1, p2;      /* Opcode used to terminate the loop */
  int iLeftJoin;       /* Memory cell used to implement LEFT OUTER JOIN */
  int top;             /* First instruction of interior of the loop */
  int inOp, inP1, inP2;/* Opcode used to implement an IN operator */

};

/*
** The WHERE clause processing routine has two halves.  The
** first part does the start of the WHERE loop and the second
** half does the tail of the WHERE loop.  An instance of
** this structure is returned by the first half and passed

**    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.
**
*************************************************************************
** Internal interface definitions for SQLite.
**
** @(#) $Id: sqliteInt.h,v 1.150 2002/12/04 20:01:06 drh Exp $
*/
#include "config.h"
#include "sqlite.h"
#include "hash.h"
#include "vdbe.h"
#include "parse.h"
#include "btree.h"
................................................................................
  int score;           /* How well this indexed scored */
  int brk;             /* Jump here to break out of the loop */
  int cont;            /* Jump here to continue with the next loop cycle */
  int op, p1, p2;      /* Opcode used to terminate the loop */
  int iLeftJoin;       /* Memory cell used to implement LEFT OUTER JOIN */
  int top;             /* First instruction of interior of the loop */
  int inOp, inP1, inP2;/* Opcode used to implement an IN operator */
  int bRev;            /* Do the scan in the reverse direction */
};

/*
** The WHERE clause processing routine has two halves.  The
** first part does the start of the WHERE loop and the second
** half does the tail of the WHERE loop.  An instance of
** this structure is returned by the first half and passed

**
** Various scripts scan this source file in order to generate HTML
** documentation, headers files, or other derived files.  The formatting
** of the code in this file is, therefore, important.  See other comments
** in this file for details.  If in doubt, do not deviate from existing
** commenting and indentation practices when changing or adding code.
**
** $Id: vdbe.c,v 1.185 2002/12/02 04:25:21 drh Exp $
*/
#include "sqliteInt.h"
#include <ctype.h>

/*
** The makefile scans this source file and creates the following
** array of string constants which are the names of all VDBE opcodes.
................................................................................
** Pop the top of the stack and use its value as a key.  Reposition
** cursor P1 so that it points to an entry with a matching key.  If
** the table contains no record with a matching key, then the cursor
** is left pointing at the first record that is greater than the key.
** If there are no records greater than the key and P2 is not zero,
** then an immediate jump to P2 is made.
**
** See also: Found, NotFound, Distinct
*/











case OP_MoveTo: {
  int i = pOp->p1;
  int tos = p->tos;
  Cursor *pC;

  VERIFY( if( tos<0 ) goto not_enough_stack; )
  if( i>=0 && i<p->nCursor && (pC = &p->aCsr[i])->pCursor!=0 ){
    int res;
    if( aStack[tos].flags & STK_Int ){
      int iKey = intToKey(aStack[tos].i);
      sqliteBtreeMoveto(pC->pCursor, (char*)&iKey, sizeof(int), &res);
      pC->lastRecno = aStack[tos].i;
      pC->recnoIsValid = res==0;
    }else{
      if( Stringify(p, tos) ) goto no_mem;
      sqliteBtreeMoveto(pC->pCursor, zStack[tos], aStack[tos].n, &res);
      pC->recnoIsValid = 0;
    }
    pC->nullRow = 0;
    sqlite_search_count++;

    if( res<0 ){
      sqliteBtreeNext(pC->pCursor, &res);
      pC->recnoIsValid = 0;
      if( res && pOp->p2>0 ){
        pc = pOp->p2 - 1;






      }
    }
  }
  POPSTACK;
  break;
}

................................................................................

/* Opcode: Next P1 P2 *
**
** Advance cursor P1 so that it points to the next key/data pair in its
** table or index.  If there are no more key/value pairs then fall through
** to the following instruction.  But if the cursor advance was successful,
** jump immediately to P2.


*/








case OP_Next: {
  int i = pOp->p1;
  BtCursor *pCrsr;

  if( VERIFY( i>=0 && i<p->nCursor && ) (pCrsr = p->aCsr[i].pCursor)!=0 ){
    int res;
    if( p->aCsr[i].nullRow ){
      res = 1;
    }else{
      rc = sqliteBtreeNext(pCrsr, &res);

      p->aCsr[i].nullRow = res;
    }
    if( res==0 ){
      pc = pOp->p2 - 1;
      sqlite_search_count++;
    }
    p->aCsr[i].recnoIsValid = 0;
................................................................................
** Compare the top of the stack against the key on the index entry that
** cursor P1 is currently pointing to.  Ignore the last 4 bytes of the
** index entry.  If the index entry is greater than or equal to 
** the top of the stack
** then jump to P2.  Otherwise fall through to the next instruction.
** In either case, the stack is popped once.
*/









case OP_IdxGT:
case OP_IdxGE: {
  int i= pOp->p1;
  int tos = p->tos;
  BtCursor *pCrsr;

  if( VERIFY( i>=0 && i<p->nCursor && ) (pCrsr = p->aCsr[i].pCursor)!=0 ){
................................................................................
    int res, rc;
 
    if( Stringify(p, tos) ) goto no_mem;
    rc = sqliteBtreeKeyCompare(pCrsr, zStack[tos], aStack[tos].n, 4, &res);
    if( rc!=SQLITE_OK ){
      break;
    }


    if( pOp->opcode==OP_IdxGE ){
      res++;
    }
    if( res>0 ){
      pc = pOp->p2 - 1 ;
    }
  }
  POPSTACK;

**
** Various scripts scan this source file in order to generate HTML
** documentation, headers files, or other derived files.  The formatting
** of the code in this file is, therefore, important.  See other comments
** in this file for details.  If in doubt, do not deviate from existing
** commenting and indentation practices when changing or adding code.
**
** $Id: vdbe.c,v 1.186 2002/12/04 20:01:06 drh Exp $
*/
#include "sqliteInt.h"
#include <ctype.h>

/*
** The makefile scans this source file and creates the following
** array of string constants which are the names of all VDBE opcodes.
................................................................................
** Pop the top of the stack and use its value as a key.  Reposition
** cursor P1 so that it points to an entry with a matching key.  If
** the table contains no record with a matching key, then the cursor
** is left pointing at the first record that is greater than the key.
** If there are no records greater than the key and P2 is not zero,
** then an immediate jump to P2 is made.
**
** See also: Found, NotFound, Distinct, MoveLt
*/
/* Opcode: MoveLt P1 P2 *
**
** Pop the top of the stack and use its value as a key.  Reposition
** cursor P1 so that it points to the entry with the largest key that is
** less than the key popped from the stack.
** If there are no records less than than the key and P2
** is not zero then an immediate jump to P2 is made.
**
** See also: MoveTo
*/
case OP_MoveLt:
case OP_MoveTo: {
  int i = pOp->p1;
  int tos = p->tos;
  Cursor *pC;

  VERIFY( if( tos<0 ) goto not_enough_stack; )
  if( i>=0 && i<p->nCursor && (pC = &p->aCsr[i])->pCursor!=0 ){
    int res, oc;
    if( aStack[tos].flags & STK_Int ){
      int iKey = intToKey(aStack[tos].i);
      sqliteBtreeMoveto(pC->pCursor, (char*)&iKey, sizeof(int), &res);
      pC->lastRecno = aStack[tos].i;
      pC->recnoIsValid = res==0;
    }else{
      if( Stringify(p, tos) ) goto no_mem;
      sqliteBtreeMoveto(pC->pCursor, zStack[tos], aStack[tos].n, &res);
      pC->recnoIsValid = 0;
    }
    pC->nullRow = 0;
    sqlite_search_count++;
    oc = pOp->opcode;
    if( oc==OP_MoveTo && res<0 ){
      sqliteBtreeNext(pC->pCursor, &res);
      pC->recnoIsValid = 0;
      if( res && pOp->p2>0 ){
        pc = pOp->p2 - 1;
      }
    }else if( oc==OP_MoveLt && res>=0 ){
      sqliteBtreePrevious(pC->pCursor, &res);
      pC->recnoIsValid = 0;
      if( res && pOp->p2>0 ){
        pc = pOp->p2 - 1;
      }
    }
  }
  POPSTACK;
  break;
}

................................................................................

/* Opcode: Next P1 P2 *
**
** Advance cursor P1 so that it points to the next key/data pair in its
** table or index.  If there are no more key/value pairs then fall through
** to the following instruction.  But if the cursor advance was successful,
** jump immediately to P2.
**
** See also: Prev
*/
/* Opcode: Prev P1 P2 *
**
** Back up cursor P1 so that it points to the previous key/data pair in its
** table or index.  If there is no previous key/value pairs then fall through
** to the following instruction.  But if the cursor backup was successful,
** jump immediately to P2.
*/
case OP_Prev:
case OP_Next: {
  int i = pOp->p1;
  BtCursor *pCrsr;

  if( VERIFY( i>=0 && i<p->nCursor && ) (pCrsr = p->aCsr[i].pCursor)!=0 ){
    int res;
    if( p->aCsr[i].nullRow ){
      res = 1;
    }else{
      rc = pOp->opcode==OP_Next ? sqliteBtreeNext(pCrsr, &res) :
                                  sqliteBtreePrevious(pCrsr, &res);
      p->aCsr[i].nullRow = res;
    }
    if( res==0 ){
      pc = pOp->p2 - 1;
      sqlite_search_count++;
    }
    p->aCsr[i].recnoIsValid = 0;
................................................................................
** Compare the top of the stack against the key on the index entry that
** cursor P1 is currently pointing to.  Ignore the last 4 bytes of the
** index entry.  If the index entry is greater than or equal to 
** the top of the stack
** then jump to P2.  Otherwise fall through to the next instruction.
** In either case, the stack is popped once.
*/
/* Opcode: IdxLT P1 P2 *
**
** Compare the top of the stack against the key on the index entry that
** cursor P1 is currently pointing to.  Ignore the last 4 bytes of the
** index entry.  If the index entry is less than the top of the stack
** then jump to P2.  Otherwise fall through to the next instruction.
** In either case, the stack is popped once.
*/
case OP_IdxLT:
case OP_IdxGT:
case OP_IdxGE: {
  int i= pOp->p1;
  int tos = p->tos;
  BtCursor *pCrsr;

  if( VERIFY( i>=0 && i<p->nCursor && ) (pCrsr = p->aCsr[i].pCursor)!=0 ){
................................................................................
    int res, rc;
 
    if( Stringify(p, tos) ) goto no_mem;
    rc = sqliteBtreeKeyCompare(pCrsr, zStack[tos], aStack[tos].n, 4, &res);
    if( rc!=SQLITE_OK ){
      break;
    }
    if( pOp->opcode==OP_IdxLT ){
      res = -res;
    }else if( pOp->opcode==OP_IdxGE ){
      res++;
    }
    if( res>0 ){
      pc = pOp->p2 - 1 ;
    }
  }
  POPSTACK;

**    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.  Also found here are subroutines
** to generate VDBE code to evaluate expressions.
**
** $Id: where.c,v 1.67 2002/12/03 02:22:52 drh Exp $
*/
#include "sqliteInt.h"

/*
** 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 an AND operator.
................................................................................
** If there are two or more indices that generate the correct sort order
** and pPreferredIdx is one of those indices, then return pPreferredIdx.
*/
static Index *findSortingIndex(
  Table *pTab,            /* The table to be sorted */
  int base,               /* Cursor number for pTab */
  ExprList *pOrderBy,     /* The ORDER BY clause */
  Index *pPreferredIdx    /* Use this index, if possible and not NULL */

){
  int i;
  Index *pMatch;
  Index *pIdx;


  assert( pOrderBy!=0 );
  assert( pOrderBy->nExpr>0 );

  for(i=0; i<pOrderBy->nExpr; i++){
    Expr *p;
    if( (pOrderBy->a[i].sortOrder & SQLITE_SO_DIRMASK)!=SQLITE_SO_ASC ){
      /* Indices can only be used for ascending sort order */

      return 0;
    }
    if( (pOrderBy->a[i].sortOrder & SQLITE_SO_TYPEMASK)!=SQLITE_SO_UNK ){
      /* Do not sort by index if there is a COLLATE clause */
      return 0;
    }
    p = pOrderBy->a[i].pExpr;
    if( p->op!=TK_COLUMN || p->iTable!=base ){
      /* Can not use an index sort on anything that is not a column in the
      ** left-most table of the FROM clause */
      return 0;
    }
  }

  /* If we get this far, it means the ORDER BY clause consists only of
  ** ascending columns in the left-most table of the FROM clause.  Now
  ** check for a matching index.
  */
  pMatch = 0;
  for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
    if( pIdx->nColumn<pOrderBy->nExpr ) continue;
................................................................................
      if( pOrderBy->a[i].pExpr->iColumn!=pIdx->aiColumn[i] ) break;
    }
    if( i>=pOrderBy->nExpr ){
      pMatch = pIdx;
      if( pIdx==pPreferredIdx ) break;
    }
  }



  return pMatch;
}

/*
** 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
................................................................................

    /* Do a search for usable indices.  Leave pBestIdx pointing to
    ** the "best" index.  pBestIdx is left set to NULL if no indices
    ** are usable.
    **
    ** The best index is determined as follows.  For each of the
    ** left-most terms that is fixed by an equality operator, add
    ** 4 to the score.  The right-most term of the index may be
    ** constrained by an inequality.  Add 1 if for an "x<..." constraint
    ** and add 2 for an "x>..." constraint.  Chose the index that
    ** gives the best score.
    **
    ** This scoring system is designed so that the score can later be
    ** used to determine how the index is used.  If the score&3 is 0
    ** then all constraints are equalities.  If score&1 is not 0 then
    ** there is an inequality used as a termination key.  (ex: "x<...")
    ** If score&2 is not 0 then there is an inequality used as the
    ** start key.  (ex: "x>...");

    **
    ** The IN operator (as in "<expr> IN (...)") is treated the same as
    ** an equality comparison except that it can only be used on the
    ** left-most column of an index and other terms of the WHERE clause
    ** cannot be used in conjunction with the IN operator to help satisfy
    ** other columns of the index.
    */
................................................................................
                }
              }
              break;
            }
          }
        }
      }




      for(nEq=0; nEq<pIdx->nColumn; nEq++){
        m = (1<<(nEq+1))-1;
        if( (m & eqMask)!=m ) break;
      }
      score = nEq*4;
      m = 1<<nEq;
      if( m & ltMask ) score++;
      if( m & gtMask ) score+=2;
      if( score==0 && inMask ) score = 4;
      if( score>bestScore ){
        pBestIdx = pIdx;
        bestScore = score;
      }
    }
    pWInfo->a[i].pIdx = pBestIdx;
    pWInfo->a[i].score = bestScore;

    loopMask |= 1<<idx;
    if( pBestIdx ){
      pWInfo->a[i].iCur = pParse->nTab++;
      pWInfo->peakNTab = pParse->nTab;
    }
  }

................................................................................
  /* Check to see if the ORDER BY clause is or can be satisfied by the
  ** use of an index on the first table.
  */
  if( ppOrderBy && *ppOrderBy && pTabList->nSrc>0 ){
     Index *pSortIdx;
     Index *pIdx;
     Table *pTab;


     pTab = pTabList->a[0].pTab;
     pIdx = pWInfo->a[0].pIdx;
     if( pIdx && pWInfo->a[0].score==4 ){
       /* If there is already an index on the left-most column and it is
       ** an equality index, then either sorting is not helpful, or the
       ** index is an IN operator, in which case the index does not give
       ** the correct sort order.  Either way, pretend that no suitable
       ** index is found.
       */
       pSortIdx = 0;
     }else if( iDirectEq[0]>=0 || iDirectLt[0]>=0 || iDirectGt[0]>=0 ){
       /* If the left-most column is accessed using its ROWID, then do
       ** not try to sort by index.
       */
       pSortIdx = 0;
     }else{
       pSortIdx = findSortingIndex(pTab, base, *ppOrderBy, pIdx);
     }
     if( pSortIdx && (pIdx==0 || pIdx==pSortIdx) ){
       if( pIdx==0 ){
         pWInfo->a[0].pIdx = pSortIdx;
         pWInfo->a[0].iCur = pParse->nTab++;
         pWInfo->peakNTab = pParse->nTab;
       }

       *ppOrderBy = 0;
     }
  }

  /* Open all tables in the pTabList and all indices used by those tables.
  */
  for(i=0; i<pTabList->nSrc; i++){
................................................................................
      pLevel->op = OP_Noop;
    }else if( pIdx!=0 && pLevel->score>0 && pLevel->score%4==0 ){
      /* Case 2:  There is an index and all terms of the WHERE clause that
      **          refer to the index use the "==" or "IN" operators.
      */
      int start;
      int testOp;
      int nColumn = pLevel->score/4;
      brk = pLevel->brk = sqliteVdbeMakeLabel(v);
      for(j=0; j<nColumn; j++){
        for(k=0; k<nExpr; k++){
          Expr *pX = aExpr[k].p;
          if( pX==0 ) continue;
          if( aExpr[k].idxLeft==idx 
             && (aExpr[k].prereqRight & loopMask)==aExpr[k].prereqRight 
................................................................................
          }
        }
      }
      pLevel->iMem = pParse->nMem++;
      cont = pLevel->cont = sqliteVdbeMakeLabel(v);
      sqliteVdbeAddOp(v, OP_MakeKey, nColumn, 0);
      sqliteAddIdxKeyType(v, pIdx);
      if( nColumn==pIdx->nColumn ){
        sqliteVdbeAddOp(v, OP_MemStore, pLevel->iMem, 0);
        testOp = OP_IdxGT;
      }else{
        sqliteVdbeAddOp(v, OP_Dup, 0, 0);
        sqliteVdbeAddOp(v, OP_IncrKey, 0, 0);
        sqliteVdbeAddOp(v, OP_MemStore, pLevel->iMem, 1);
        testOp = OP_IdxGE;
      }










      sqliteVdbeAddOp(v, OP_MoveTo, pLevel->iCur, brk);
      start = sqliteVdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
      sqliteVdbeAddOp(v, testOp, pLevel->iCur, brk);
      sqliteVdbeAddOp(v, OP_IdxRecno, pLevel->iCur, 0);


      if( i==pTabList->nSrc-1 && pushKey ){
        haveKey = 1;
      }else{
        sqliteVdbeAddOp(v, OP_MoveTo, base+idx, 0);
        haveKey = 0;
      }
      pLevel->op = OP_Next;
      pLevel->p1 = pLevel->iCur;
      pLevel->p2 = start;
    }else if( i<ARRAYSIZE(iDirectLt) && (iDirectLt[i]>=0 || iDirectGt[i]>=0) ){
      /* Case 3:  We have an inequality comparison against the ROWID field.
      */
      int testOp = OP_Noop;
      int start;
................................................................................
      **         use the "==" operator.
      **
      **         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.
      */
      int score = pLevel->score;
      int nEqColumn = score/4;
      int start;
      int leFlag, geFlag;
      int testOp;

      /* Evaluate the equality constraints
      */
      for(j=0; j<nEqColumn; j++){
................................................................................
      /* Duplicate the equality term values because they will all be
      ** used twice: once to make the termination key and once to make the
      ** start key.
      */
      for(j=0; j<nEqColumn; j++){
        sqliteVdbeAddOp(v, OP_Dup, nEqColumn-1, 0);
      }






      /* Generate the termination key.  This is the key value that
      ** will end the search.  There is no termination key if there
      ** are no equality terms and no "X<..." term.



      */
      if( (score & 1)!=0 ){
        for(k=0; k<nExpr; k++){
          Expr *pExpr = aExpr[k].p;
          if( pExpr==0 ) continue;
          if( aExpr[k].idxLeft==idx 
             && (pExpr->op==TK_LT || pExpr->op==TK_LE)
................................................................................
      if( testOp!=OP_Noop ){
        pLevel->iMem = pParse->nMem++;
        sqliteVdbeAddOp(v, OP_MakeKey, nEqColumn + (score & 1), 0);
        sqliteAddIdxKeyType(v, pIdx);
        if( leFlag ){
          sqliteVdbeAddOp(v, OP_IncrKey, 0, 0);
        }



        sqliteVdbeAddOp(v, OP_MemStore, pLevel->iMem, 1);



      }

      /* Generate the start key.  This is the key that defines the lower
      ** bound on the search.  There is no start key if there are no
      ** equality terms and if there is no "X>..." term.  In
      ** that case, generate a "Rewind" instruction in place of the
      ** start key search.



      */
      if( (score & 2)!=0 ){
        for(k=0; k<nExpr; k++){
          Expr *pExpr = aExpr[k].p;
          if( pExpr==0 ) continue;
          if( aExpr[k].idxLeft==idx 
             && (pExpr->op==TK_GT || pExpr->op==TK_GE)
................................................................................
            aExpr[k].p = 0;
            break;
          }
        }
      }else{
        geFlag = 1;
      }
      brk = pLevel->brk = sqliteVdbeMakeLabel(v);
      cont = pLevel->cont = sqliteVdbeMakeLabel(v);
      if( nEqColumn>0 || (score&2)!=0 ){
        sqliteVdbeAddOp(v, OP_MakeKey, nEqColumn + ((score&2)!=0), 0);
        sqliteAddIdxKeyType(v, pIdx);
        if( !geFlag ){
          sqliteVdbeAddOp(v, OP_IncrKey, 0, 0);
        }





        sqliteVdbeAddOp(v, OP_MoveTo, pLevel->iCur, brk);



      }else{
        sqliteVdbeAddOp(v, OP_Rewind, pLevel->iCur, brk);
      }

      /* Generate the the top of the loop.  If there is a termination
      ** key we have to test for that key and abort at the top of the
      ** loop.
................................................................................
      }else{
        sqliteVdbeAddOp(v, OP_MoveTo, base+idx, 0);
        haveKey = 0;
      }

      /* Record the instruction used to terminate the loop.
      */
      pLevel->op = OP_Next;
      pLevel->p1 = pLevel->iCur;
      pLevel->p2 = start;
    }
    loopMask |= 1<<idx;

    /* Insert code to test every subexpression that can be completely
    ** computed using the current set of tables.

**    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.  Also found here are subroutines
** to generate VDBE code to evaluate expressions.
**
** $Id: where.c,v 1.68 2002/12/04 20:01:06 drh Exp $
*/
#include "sqliteInt.h"

/*
** 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 an AND operator.
................................................................................
** If there are two or more indices that generate the correct sort order
** and pPreferredIdx is one of those indices, then return pPreferredIdx.
*/
static Index *findSortingIndex(
  Table *pTab,            /* The table to be sorted */
  int base,               /* Cursor number for pTab */
  ExprList *pOrderBy,     /* The ORDER BY clause */
  Index *pPreferredIdx,   /* Use this index, if possible and not NULL */
  int *pbRev              /* Set to 1 if ORDER BY is DESC */
){
  int i;
  Index *pMatch;
  Index *pIdx;
  int sortOrder;

  assert( pOrderBy!=0 );
  assert( pOrderBy->nExpr>0 );
  sortOrder = pOrderBy->a[0].sortOrder & SQLITE_SO_DIRMASK;
  for(i=0; i<pOrderBy->nExpr; i++){
    Expr *p;
    if( (pOrderBy->a[i].sortOrder & SQLITE_SO_DIRMASK)!=sortOrder ){
      /* Indices can only be used if all ORDER BY terms are either
      ** DESC or ASC.  Indices cannot be used on a mixture. */
      return 0;
    }
    if( (pOrderBy->a[i].sortOrder & SQLITE_SO_TYPEMASK)!=SQLITE_SO_UNK ){
      /* Do not sort by index if there is a COLLATE clause */
      return 0;
    }
    p = pOrderBy->a[i].pExpr;
    if( p->op!=TK_COLUMN || p->iTable!=base ){
      /* Can not use an index sort on anything that is not a column in the
      ** left-most table of the FROM clause */
      return 0;
    }
  }
  
  /* If we get this far, it means the ORDER BY clause consists only of
  ** ascending columns in the left-most table of the FROM clause.  Now
  ** check for a matching index.
  */
  pMatch = 0;
  for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
    if( pIdx->nColumn<pOrderBy->nExpr ) continue;
................................................................................
      if( pOrderBy->a[i].pExpr->iColumn!=pIdx->aiColumn[i] ) break;
    }
    if( i>=pOrderBy->nExpr ){
      pMatch = pIdx;
      if( pIdx==pPreferredIdx ) break;
    }
  }
  if( pMatch && pbRev ){
    *pbRev = sortOrder==SQLITE_SO_DESC;
  }
  return pMatch;
}

/*
** 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
................................................................................

    /* Do a search for usable indices.  Leave pBestIdx pointing to
    ** the "best" index.  pBestIdx is left set to NULL if no indices
    ** are usable.
    **
    ** The best index is determined as follows.  For each of the
    ** left-most terms that is fixed by an equality operator, add
    ** 8 to the score.  The right-most term of the index may be
    ** constrained by an inequality.  Add 1 if for an "x<..." constraint
    ** and add 2 for an "x>..." constraint.  Chose the index that
    ** gives the best score.
    **
    ** This scoring system is designed so that the score can later be
    ** used to determine how the index is used.  If the score&7 is 0
    ** then all constraints are equalities.  If score&1 is not 0 then
    ** there is an inequality used as a termination key.  (ex: "x<...")
    ** If score&2 is not 0 then there is an inequality used as the
    ** start key.  (ex: "x>...").  A score or 4 is the special case
    ** of an IN operator constraint.  (ex:  "x IN ...").
    **
    ** The IN operator (as in "<expr> IN (...)") is treated the same as
    ** an equality comparison except that it can only be used on the
    ** left-most column of an index and other terms of the WHERE clause
    ** cannot be used in conjunction with the IN operator to help satisfy
    ** other columns of the index.
    */
................................................................................
                }
              }
              break;
            }
          }
        }
      }

      /* The following loop ends with nEq set to the number of columns
      ** on the left of the index with == constraints.
      */
      for(nEq=0; nEq<pIdx->nColumn; nEq++){
        m = (1<<(nEq+1))-1;
        if( (m & eqMask)!=m ) break;
      }
      score = nEq*8;   /* Base score is 8 times number of == constraints */
      m = 1<<nEq;
      if( m & ltMask ) score++;    /* Increase score for a < constraint */
      if( m & gtMask ) score+=2;   /* Increase score for a > constraint */
      if( score==0 && inMask ) score = 4;  /* Default score for IN constraint */
      if( score>bestScore ){
        pBestIdx = pIdx;
        bestScore = score;
      }
    }
    pWInfo->a[i].pIdx = pBestIdx;
    pWInfo->a[i].score = bestScore;
    pWInfo->a[i].bRev = 0;
    loopMask |= 1<<idx;
    if( pBestIdx ){
      pWInfo->a[i].iCur = pParse->nTab++;
      pWInfo->peakNTab = pParse->nTab;
    }
  }

................................................................................
  /* Check to see if the ORDER BY clause is or can be satisfied by the
  ** use of an index on the first table.
  */
  if( ppOrderBy && *ppOrderBy && pTabList->nSrc>0 ){
     Index *pSortIdx;
     Index *pIdx;
     Table *pTab;
     int bRev = 0;

     pTab = pTabList->a[0].pTab;
     pIdx = pWInfo->a[0].pIdx;
     if( pIdx && pWInfo->a[0].score==4 ){
       /* If there is already an IN index on the left-most table,
       ** it will not give the correct sort order.

       ** So, pretend that no suitable index is found.

       */
       pSortIdx = 0;
     }else if( iDirectEq[0]>=0 || iDirectLt[0]>=0 || iDirectGt[0]>=0 ){
       /* If the left-most column is accessed using its ROWID, then do
       ** not try to sort by index.
       */
       pSortIdx = 0;
     }else{
       pSortIdx = findSortingIndex(pTab, base, *ppOrderBy, pIdx, &bRev);
     }
     if( pSortIdx && (pIdx==0 || pIdx==pSortIdx) ){
       if( pIdx==0 ){
         pWInfo->a[0].pIdx = pSortIdx;
         pWInfo->a[0].iCur = pParse->nTab++;
         pWInfo->peakNTab = pParse->nTab;
       }
       pWInfo->a[0].bRev = bRev;
       *ppOrderBy = 0;
     }
  }

  /* Open all tables in the pTabList and all indices used by those tables.
  */
  for(i=0; i<pTabList->nSrc; i++){
................................................................................
      pLevel->op = OP_Noop;
    }else if( pIdx!=0 && pLevel->score>0 && pLevel->score%4==0 ){
      /* Case 2:  There is an index and all terms of the WHERE clause that
      **          refer to the index use the "==" or "IN" operators.
      */
      int start;
      int testOp;
      int nColumn = (pLevel->score+4)/8;
      brk = pLevel->brk = sqliteVdbeMakeLabel(v);
      for(j=0; j<nColumn; j++){
        for(k=0; k<nExpr; k++){
          Expr *pX = aExpr[k].p;
          if( pX==0 ) continue;
          if( aExpr[k].idxLeft==idx 
             && (aExpr[k].prereqRight & loopMask)==aExpr[k].prereqRight 
................................................................................
          }
        }
      }
      pLevel->iMem = pParse->nMem++;
      cont = pLevel->cont = sqliteVdbeMakeLabel(v);
      sqliteVdbeAddOp(v, OP_MakeKey, nColumn, 0);
      sqliteAddIdxKeyType(v, pIdx);
      if( nColumn==pIdx->nColumn || pLevel->bRev ){
        sqliteVdbeAddOp(v, OP_MemStore, pLevel->iMem, 0);
        testOp = OP_IdxGT;
      }else{
        sqliteVdbeAddOp(v, OP_Dup, 0, 0);
        sqliteVdbeAddOp(v, OP_IncrKey, 0, 0);
        sqliteVdbeAddOp(v, OP_MemStore, pLevel->iMem, 1);
        testOp = OP_IdxGE;
      }
      if( pLevel->bRev ){
        /* Scan in reverse order */
        sqliteVdbeAddOp(v, OP_IncrKey, 0, 0);
        sqliteVdbeAddOp(v, OP_MoveLt, pLevel->iCur, brk);
        start = sqliteVdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
        sqliteVdbeAddOp(v, OP_IdxLT, pLevel->iCur, brk);
        sqliteVdbeAddOp(v, OP_IdxRecno, pLevel->iCur, 0);
        pLevel->op = OP_Prev;
      }else{
        /* Scan in the forward order */
        sqliteVdbeAddOp(v, OP_MoveTo, pLevel->iCur, brk);
        start = sqliteVdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
        sqliteVdbeAddOp(v, testOp, pLevel->iCur, brk);
        sqliteVdbeAddOp(v, OP_IdxRecno, pLevel->iCur, 0);
        pLevel->op = OP_Next;
      }
      if( i==pTabList->nSrc-1 && pushKey ){
        haveKey = 1;
      }else{
        sqliteVdbeAddOp(v, OP_MoveTo, base+idx, 0);
        haveKey = 0;
      }

      pLevel->p1 = pLevel->iCur;
      pLevel->p2 = start;
    }else if( i<ARRAYSIZE(iDirectLt) && (iDirectLt[i]>=0 || iDirectGt[i]>=0) ){
      /* Case 3:  We have an inequality comparison against the ROWID field.
      */
      int testOp = OP_Noop;
      int start;
................................................................................
      **         use the "==" operator.
      **
      **         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.
      */
      int score = pLevel->score;
      int nEqColumn = score/8;
      int start;
      int leFlag, geFlag;
      int testOp;

      /* Evaluate the equality constraints
      */
      for(j=0; j<nEqColumn; j++){
................................................................................
      /* Duplicate the equality term values because they will all be
      ** used twice: once to make the termination key and once to make the
      ** start key.
      */
      for(j=0; j<nEqColumn; j++){
        sqliteVdbeAddOp(v, OP_Dup, nEqColumn-1, 0);
      }

      /* Labels for the beginning and end of the loop
      */
      cont = pLevel->cont = sqliteVdbeMakeLabel(v);
      brk = pLevel->brk = sqliteVdbeMakeLabel(v);

      /* Generate the termination key.  This is the key value that
      ** will end the search.  There is no termination key if there
      ** are no equality terms and no "X<..." term.
      **
      ** 2002-Dec-04: On a reverse-order scan, the so-called "termination"
      ** key computed here really ends up being the start key.
      */
      if( (score & 1)!=0 ){
        for(k=0; k<nExpr; k++){
          Expr *pExpr = aExpr[k].p;
          if( pExpr==0 ) continue;
          if( aExpr[k].idxLeft==idx 
             && (pExpr->op==TK_LT || pExpr->op==TK_LE)
................................................................................
      if( testOp!=OP_Noop ){
        pLevel->iMem = pParse->nMem++;
        sqliteVdbeAddOp(v, OP_MakeKey, nEqColumn + (score & 1), 0);
        sqliteAddIdxKeyType(v, pIdx);
        if( leFlag ){
          sqliteVdbeAddOp(v, OP_IncrKey, 0, 0);
        }
        if( pLevel->bRev ){
          sqliteVdbeAddOp(v, OP_MoveLt, pLevel->iCur, brk);
        }else{
          sqliteVdbeAddOp(v, OP_MemStore, pLevel->iMem, 1);
        }
      }else if( pLevel->bRev ){
        sqliteVdbeAddOp(v, OP_Last, pLevel->iCur, brk);
      }

      /* Generate the start key.  This is the key that defines the lower
      ** bound on the search.  There is no start key if there are no
      ** equality terms and if there is no "X>..." term.  In
      ** that case, generate a "Rewind" instruction in place of the
      ** start key search.
      **
      ** 2002-Dec-04: In the case of a reverse-order search, the so-called
      ** "start" key really ends up being used as the termination key.
      */
      if( (score & 2)!=0 ){
        for(k=0; k<nExpr; k++){
          Expr *pExpr = aExpr[k].p;
          if( pExpr==0 ) continue;
          if( aExpr[k].idxLeft==idx 
             && (pExpr->op==TK_GT || pExpr->op==TK_GE)
................................................................................
            aExpr[k].p = 0;
            break;
          }
        }
      }else{
        geFlag = 1;
      }


      if( nEqColumn>0 || (score&2)!=0 ){
        sqliteVdbeAddOp(v, OP_MakeKey, nEqColumn + ((score&2)!=0), 0);
        sqliteAddIdxKeyType(v, pIdx);
        if( !geFlag ){
          sqliteVdbeAddOp(v, OP_IncrKey, 0, 0);
        }
        if( pLevel->bRev ){
          pLevel->iMem = pParse->nMem++;
          sqliteVdbeAddOp(v, OP_MemStore, pLevel->iMem, 1);
          testOp = OP_IdxLT;
        }else{
          sqliteVdbeAddOp(v, OP_MoveTo, pLevel->iCur, brk);
        }
      }else if( pLevel->bRev ){
        testOp = OP_Noop;
      }else{
        sqliteVdbeAddOp(v, OP_Rewind, pLevel->iCur, brk);
      }

      /* Generate the the top of the loop.  If there is a termination
      ** key we have to test for that key and abort at the top of the
      ** loop.
................................................................................
      }else{
        sqliteVdbeAddOp(v, OP_MoveTo, base+idx, 0);
        haveKey = 0;
      }

      /* Record the instruction used to terminate the loop.
      */
      pLevel->op = pLevel->bRev ? OP_Prev : OP_Next;
      pLevel->p1 = pLevel->iCur;
      pLevel->p2 = start;
    }
    loopMask |= 1<<idx;

    /* Insert code to test every subexpression that can be completely
    ** computed using the current set of tables.