SQLite

** 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_IPK          0x00004000  /* x is the INTEGER PRIMARY KEY */
#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_NOT_FULLSCAN 0x100f3000  /* Does not do a full table scan */
#define WHERE_IN_ABLE      0x080f1000  /* Able to support an IN operator */

  WhereTerm *pTerm;    /* The term being tested */

  while( pScan->iEquiv<=pScan->nEquiv ){
    iCur = pScan->aEquiv[pScan->iEquiv-2];
    iColumn = pScan->aEquiv[pScan->iEquiv-1];
    while( (pWC = pScan->pWC)!=0 ){
      for(pTerm=pWC->a+pScan->k; pScan->k<pWC->nTerm; pScan->k++, pTerm++){
        if( pTerm->iParent>=0 ){
          WhereTerm *pParent = &pWC->a[pTerm->iParent];
          int j;
          for(j=pScan->iEquiv-4; j>=0; j-=2 ){
            if( pParent->leftCursor==pScan->aEquiv[j]
             && pParent->u.leftColumn==pScan->aEquiv[j+1] ) break;
          }
          if( j>=0 ) continue;
        }
        if( pTerm->leftCursor==iCur && pTerm->u.leftColumn==iColumn ){
          if( (pTerm->eOperator & WO_EQUIV)!=0
           && pScan->nEquiv<ArraySize(pScan->aEquiv)
          ){
            int j;
            pX = sqlite3ExprSkipCollate(pTerm->pExpr->pRight);
            assert( pX->op==TK_COLUMN );

** An existing WhereLoop entry might be overwritten if the new template
** is better and has fewer dependencies.  Or the template will be ignored
** and no insert will occur if an existing WhereLoop is faster and has
** fewer dependencies than the template.  Otherwise a new WhereLoop is
** added based no the template.
*/
static int whereLoopInsert(WhereInfo *pWInfo, WhereLoop *pTemplate){
  WhereLoop **ppPrev, *p, *pNext = 0, *pToFree = 0;
  sqlite3 *db = pWInfo->pParse->db;

  /* Search for an existing WhereLoop to overwrite, or which takes
  ** priority over pTemplate.
  */
  for(ppPrev=&pWInfo->pLoops, p=*ppPrev; p; ppPrev=&p->pNextLoop, p=*ppPrev){
    if( p->iTab!=pTemplate->iTab ) continue;

     && p->nOb<=pTemplate->nOb
     && p->iOb==pTemplate->iOb
     && p->rSetup>=pTemplate->rSetup
     && p->rRun>=pTemplate->rRun
    ){
      /* Overwrite an existing WhereLoop with a better one */
      sqlite3DbFree(db, p->aTerm);
      pNext = p->pNextLoop;
      break;
    }
  }

  /* If we reach this point it means that either p[] should be overwritten
  ** with pTemplate[] if p[] exists, or if p==NULL then allocate a new
  ** WhereLoop and insert it.
  */
  if( p==0 ){
    p = pToFree = sqlite3DbMallocRaw(db, sizeof(WhereLoop));
    if( p==0 ) return SQLITE_NOMEM;
  }
  *p = *pTemplate;
  p->pNextLoop = pNext;
  *ppPrev = p;
  p->aTerm = 0;
  if( p->pIndex && p->pIndex->tnum==0 ) p->pIndex = 0;
  if( pTemplate->nTerm<=0 ) return SQLITE_OK;
  p->aTerm = sqlite3DbMallocRaw(db, pTemplate->nTerm*sizeof(p->aTerm[0]));
  if( p->aTerm==0 ){
    p->nTerm = 0;
    sqlite3DbFree(db, pToFree);
    return SQLITE_NOMEM;
  }
  memcpy(p->aTerm, pTemplate->aTerm, pTemplate->nTerm*sizeof(p->aTerm[0]));
  return SQLITE_OK;
}

/*
** We have so far matched pBuilder->pNew->nEq terms of the index pIndex.
** Try to match one more.
**
** If pProbe->tnum==0, that means pIndex is a fake index used for the
** INTEGER PRIMARY KEY.
*/
static void whereLoopAddBtreeIndex(
  WhereLoopBuilder *pBuilder,     /* The WhereLoop factory */
  Bitmask maskSelf,               /* Bitmask for table being scanned */
  struct SrcList_item *pSrc,      /* FROM clause term being analyzed */
  Index *pProbe,                  /* An index on pSrc */
  int nInMul                      /* Number of iterations due to IN */
){
  sqlite3 *db;                    /* Database connection malloc context */
  WhereLoop *pNew;                /* Template WhereLoop under construction */
  WhereTerm *pTerm;               /* A WhereTerm under consideration */
  int opMask;                     /* Valid operators for constraints */
  WhereScan scan;                 /* Iterator for WHERE terms */
  WhereLoop savedLoop;            /* Saved original content of pNew[] */

  db = pBuilder->db;
  pNew = pBuilder->pNew;
  if( db->mallocFailed ) return;

  assert( pNew->nEq<pProbe->nColumn );
  assert( (pNew->wsFlags & WHERE_TOP_LIMIT)==0 );
  if( pNew->wsFlags & WHERE_BTM_LIMIT ){
    opMask = WO_LT|WO_LE;
  }else if( pProbe->tnum<=0 || (pSrc->jointype & JT_LEFT)!=0 ){
    opMask = WO_EQ|WO_IN|WO_GT|WO_GE|WO_LT|WO_LE;
  }else{
    opMask = WO_EQ|WO_IN|WO_ISNULL|WO_GT|WO_GE|WO_LT|WO_LE;
  }


  if( pNew->nEq<pProbe->nColumn ){
    int iCol;            /* Index of the column in the table */


    iCol = pProbe->aiColumn[pNew->nEq];
    pTerm = whereScanInit(&scan, pBuilder->pWC, pSrc->iCursor, iCol,
                          opMask, iCol>=0 ? pProbe : 0);
    savedLoop = *pNew;
    pNew->rSetup = (double)0;
    for(; pTerm!=0; pTerm = whereScanNext(&scan)){
      int nIn = 1;
      pNew->nEq = savedLoop.nEq;
      pNew->nTerm = savedLoop.nTerm;

      pNew->aTerm[pNew->nTerm++] = pTerm;
      pNew->prereq = (savedLoop.prereq | pTerm->prereqRight) & ~maskSelf;
      if( pTerm->eOperator & WO_IN ){
        Expr *pExpr = pTerm->pExpr;
        pNew->wsFlags |= WHERE_COLUMN_IN;
        if( ExprHasProperty(pExpr, EP_xIsSelect) ){
          /* "x IN (SELECT ...)":  Assume the SELECT returns 25 rows */
          nIn = 25;
        }else if( ALWAYS(pExpr->x.pList && pExpr->x.pList->nExpr) ){
          /* "x IN (value, value, ...)" */
          nIn = pExpr->x.pList->nExpr;
        }
        pNew->nEq++;
        pNew->nOut = (double)pProbe->aiRowEst[pNew->nEq] * nInMul * nIn;
      }else if( pTerm->eOperator & (WO_EQ|WO_ISNULL) ){
        pNew->wsFlags |= WHERE_COLUMN_EQ;
        pNew->nEq++;
        pNew->nOut = (double)pProbe->aiRowEst[pNew->nEq] * nInMul;
      }else if( pTerm->eOperator & (WO_GT|WO_GE) ){
        pNew->wsFlags |= WHERE_COLUMN_RANGE|WHERE_BTM_LIMIT;
        pNew->nOut = savedLoop.nOut/3;
      }else if( pTerm->eOperator & (WO_LT|WO_LE) ){
        pNew->wsFlags |= WHERE_COLUMN_RANGE|WHERE_TOP_LIMIT;
        pNew->nOut = savedLoop.nOut/3;
      }
      pNew->rRun = pNew->nOut + estLog(pProbe->aiRowEst[0])*nIn;
      whereLoopInsert(pBuilder->pWInfo, pNew);
      if( (pNew->wsFlags & WHERE_TOP_LIMIT)==0 && pNew->nEq<pProbe->nColumn ){
        whereLoopAddBtreeIndex(pBuilder, maskSelf, pSrc, pProbe, nInMul*nIn);
      }
    }
    *pNew = savedLoop;
  }
}

/*

  Index *pProbe;              /* An index we are evaluating */
  Index sPk;                  /* A fake index object for the primary key */
  tRowcnt aiRowEstPk[2];      /* The aiRowEst[] value for the sPk index */
  int aiColumnPk = -1;        /* The aColumn[] value for the sPk index */
  struct SrcList_item *pSrc;  /* The FROM clause btree term to add */
  sqlite3 *db;                /* The database connection */
  WhereLoop *pNew;            /* Template WhereLoop object */
  Bitmask maskSelf;           /* Mask for iTab */

  pNew = pBuilder->pNew;
  db = pBuilder->db;
  pSrc = pBuilder->pTabList->a + iTab;
  maskSelf = getMask(pBuilder->pWC->pMaskSet, iTab);

  if( pSrc->pIndex ){
    /* An INDEXED BY clause specifies a particular index to use */
    pProbe = pSrc->pIndex;
  }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

      /* 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;
  }

  /* Insert a full table scan */
  pNew->iTab = iTab;
  pNew->nEq = 0;
  pNew->nTerm = 0;
  pNew->rSetup = (double)0;
  pNew->prereq = 0;
  pNew->pIndex = 0;
  pNew->wsFlags = 0;
  pNew->iOb = pNew->nOb = 0;
  pNew->rRun = (double)pSrc->pTab->nRowEst;
  pNew->nOut = (double)pSrc->pTab->nRowEst;
  whereLoopInsert(pBuilder->pWInfo, pNew);

  /* Loop over all indices
  */
  for(; pProbe; pProbe=pProbe->pNext){
    WhereTerm **paTerm;
    pNew->prereq = mExtra;
    pNew->iTab = iTab;
    pNew->nEq = 0;
    pNew->nTerm = 0;
    if( pProbe->tnum<=0 ){
      /* Integer primary key index */
      pNew->wsFlags = WHERE_IPK;
    }else{
      Bitmask m = pSrc->colUsed;
      int j;
      for(j=pProbe->nColumn-1; j>=0; j--){
        int x = pProbe->aiColumn[j];
        if( x<BMS-1 ){
          m &= ~(((Bitmask)1)<<x);
        }
      }
      pNew->wsFlags = m==0 ? WHERE_IDX_ONLY : 0;
    }
    paTerm = sqlite3DbRealloc(db, pNew->aTerm,
                              (pProbe->nColumn+1)*sizeof(pNew->aTerm[0]));
    if( paTerm==0 ) break;
    pNew->aTerm = paTerm;
    pNew->pIndex = pProbe;

    whereLoopAddBtreeIndex(pBuilder, maskSelf, pSrc, pProbe, 1);

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









}

/*
** Add all WhereLoop objects for the iTab-th table of the join.  That
** table is guaranteed to be a virtual table.
*/
static void whereLoopAddVirtual(

  if( sqlite3WhereTrace ){
    WhereLoop *p;
    int nb = 2*((nTabList+15)/16);
    for(p=pWInfo->pLoops; p; p=p->pNextLoop){
      struct SrcList_item *pItem = pTabList->a + p->iTab;
       Table *pTab = pItem->pTab;
      sqlite3DebugPrintf("%02d.%0*llx", p->iTab, nb, p->prereq);
      sqlite3DebugPrintf(" %6s",
                         pItem->zAlias ? pItem->zAlias : pTab->zName);
      if( p->pIndex ){
        sqlite3DebugPrintf(".%-8s %2d", p->pIndex->zName, p->nEq);
      }else{
        sqlite3DebugPrintf("%12s","");
      }
      sqlite3DebugPrintf(" fg %08x OB %d,%d N %2d",
                         p->wsFlags, p->iOb, p->nOb, p->nTerm);
      sqlite3DebugPrintf(" cost %.4g,%.4g,%.4g\n",
                         p->prereq, p->rSetup, p->rRun, p->nOut);
    }
  }
#endif

  /* Chose the best index to use for each table in the FROM clause.
  **