Annotation of embedaddon/php/ext/sqlite/libsqlite/src/where.c, revision 1.1

1.1     ! misho       1: /*
        !             2: ** 2001 September 15
        !             3: **
        !             4: ** The author disclaims copyright to this source code.  In place of
        !             5: ** a legal notice, here is a blessing:
        !             6: **
        !             7: **    May you do good and not evil.
        !             8: **    May you find forgiveness for yourself and forgive others.
        !             9: **    May you share freely, never taking more than you give.
        !            10: **
        !            11: *************************************************************************
        !            12: ** This module contains C code that generates VDBE code used to process
        !            13: ** the WHERE clause of SQL statements.
        !            14: **
        !            15: ** $Id: where.c 195361 2005-09-07 15:11:33Z iliaa $
        !            16: */
        !            17: #include "sqliteInt.h"
        !            18: 
        !            19: /*
        !            20: ** The query generator uses an array of instances of this structure to
        !            21: ** help it analyze the subexpressions of the WHERE clause.  Each WHERE
        !            22: ** clause subexpression is separated from the others by an AND operator.
        !            23: */
        !            24: typedef struct ExprInfo ExprInfo;
        !            25: struct ExprInfo {
        !            26:   Expr *p;                /* Pointer to the subexpression */
        !            27:   u8 indexable;           /* True if this subexprssion is usable by an index */
        !            28:   short int idxLeft;      /* p->pLeft is a column in this table number. -1 if
        !            29:                           ** p->pLeft is not the column of any table */
        !            30:   short int idxRight;     /* p->pRight is a column in this table number. -1 if
        !            31:                           ** p->pRight is not the column of any table */
        !            32:   unsigned prereqLeft;    /* Bitmask of tables referenced by p->pLeft */
        !            33:   unsigned prereqRight;   /* Bitmask of tables referenced by p->pRight */
        !            34:   unsigned prereqAll;     /* Bitmask of tables referenced by p */
        !            35: };
        !            36: 
        !            37: /*
        !            38: ** An instance of the following structure keeps track of a mapping
        !            39: ** between VDBE cursor numbers and bitmasks.  The VDBE cursor numbers
        !            40: ** are small integers contained in SrcList_item.iCursor and Expr.iTable
        !            41: ** fields.  For any given WHERE clause, we want to track which cursors
        !            42: ** are being used, so we assign a single bit in a 32-bit word to track
        !            43: ** that cursor.  Then a 32-bit integer is able to show the set of all
        !            44: ** cursors being used.
        !            45: */
        !            46: typedef struct ExprMaskSet ExprMaskSet;
        !            47: struct ExprMaskSet {
        !            48:   int n;          /* Number of assigned cursor values */
        !            49:   int ix[31];     /* Cursor assigned to each bit */
        !            50: };
        !            51: 
        !            52: /*
        !            53: ** Determine the number of elements in an array.
        !            54: */
        !            55: #define ARRAYSIZE(X)  (sizeof(X)/sizeof(X[0]))
        !            56: 
        !            57: /*
        !            58: ** This routine is used to divide the WHERE expression into subexpressions
        !            59: ** separated by the AND operator.
        !            60: **
        !            61: ** aSlot[] is an array of subexpressions structures.
        !            62: ** There are nSlot spaces left in this array.  This routine attempts to
        !            63: ** split pExpr into subexpressions and fills aSlot[] with those subexpressions.
        !            64: ** The return value is the number of slots filled.
        !            65: */
        !            66: static int exprSplit(int nSlot, ExprInfo *aSlot, Expr *pExpr){
        !            67:   int cnt = 0;
        !            68:   if( pExpr==0 || nSlot<1 ) return 0;
        !            69:   if( nSlot==1 || pExpr->op!=TK_AND ){
        !            70:     aSlot[0].p = pExpr;
        !            71:     return 1;
        !            72:   }
        !            73:   if( pExpr->pLeft->op!=TK_AND ){
        !            74:     aSlot[0].p = pExpr->pLeft;
        !            75:     cnt = 1 + exprSplit(nSlot-1, &aSlot[1], pExpr->pRight);
        !            76:   }else{
        !            77:     cnt = exprSplit(nSlot, aSlot, pExpr->pLeft);
        !            78:     cnt += exprSplit(nSlot-cnt, &aSlot[cnt], pExpr->pRight);
        !            79:   }
        !            80:   return cnt;
        !            81: }
        !            82: 
        !            83: /*
        !            84: ** Initialize an expression mask set
        !            85: */
        !            86: #define initMaskSet(P)  memset(P, 0, sizeof(*P))
        !            87: 
        !            88: /*
        !            89: ** Return the bitmask for the given cursor.  Assign a new bitmask
        !            90: ** if this is the first time the cursor has been seen.
        !            91: */
        !            92: static int getMask(ExprMaskSet *pMaskSet, int iCursor){
        !            93:   int i;
        !            94:   for(i=0; i<pMaskSet->n; i++){
        !            95:     if( pMaskSet->ix[i]==iCursor ) return 1<<i;
        !            96:   }
        !            97:   if( i==pMaskSet->n && i<ARRAYSIZE(pMaskSet->ix) ){
        !            98:     pMaskSet->n++;
        !            99:     pMaskSet->ix[i] = iCursor;
        !           100:     return 1<<i;
        !           101:   }
        !           102:   return 0;
        !           103: }
        !           104: 
        !           105: /*
        !           106: ** Destroy an expression mask set
        !           107: */
        !           108: #define freeMaskSet(P)   /* NO-OP */
        !           109: 
        !           110: /*
        !           111: ** This routine walks (recursively) an expression tree and generates
        !           112: ** a bitmask indicating which tables are used in that expression
        !           113: ** tree.
        !           114: **
        !           115: ** In order for this routine to work, the calling function must have
        !           116: ** previously invoked sqliteExprResolveIds() on the expression.  See
        !           117: ** the header comment on that routine for additional information.
        !           118: ** The sqliteExprResolveIds() routines looks for column names and
        !           119: ** sets their opcodes to TK_COLUMN and their Expr.iTable fields to
        !           120: ** the VDBE cursor number of the table.
        !           121: */
        !           122: static int exprTableUsage(ExprMaskSet *pMaskSet, Expr *p){
        !           123:   unsigned int mask = 0;
        !           124:   if( p==0 ) return 0;
        !           125:   if( p->op==TK_COLUMN ){
        !           126:     mask = getMask(pMaskSet, p->iTable);
        !           127:     if( mask==0 ) mask = -1;
        !           128:     return mask;
        !           129:   }
        !           130:   if( p->pRight ){
        !           131:     mask = exprTableUsage(pMaskSet, p->pRight);
        !           132:   }
        !           133:   if( p->pLeft ){
        !           134:     mask |= exprTableUsage(pMaskSet, p->pLeft);
        !           135:   }
        !           136:   if( p->pList ){
        !           137:     int i;
        !           138:     for(i=0; i<p->pList->nExpr; i++){
        !           139:       mask |= exprTableUsage(pMaskSet, p->pList->a[i].pExpr);
        !           140:     }
        !           141:   }
        !           142:   return mask;
        !           143: }
        !           144: 
        !           145: /*
        !           146: ** Return TRUE if the given operator is one of the operators that is
        !           147: ** allowed for an indexable WHERE clause.  The allowed operators are
        !           148: ** "=", "<", ">", "<=", ">=", and "IN".
        !           149: */
        !           150: static int allowedOp(int op){
        !           151:   switch( op ){
        !           152:     case TK_LT:
        !           153:     case TK_LE:
        !           154:     case TK_GT:
        !           155:     case TK_GE:
        !           156:     case TK_EQ:
        !           157:     case TK_IN:
        !           158:       return 1;
        !           159:     default:
        !           160:       return 0;
        !           161:   }
        !           162: }
        !           163: 
        !           164: /*
        !           165: ** The input to this routine is an ExprInfo structure with only the
        !           166: ** "p" field filled in.  The job of this routine is to analyze the
        !           167: ** subexpression and populate all the other fields of the ExprInfo
        !           168: ** structure.
        !           169: */
        !           170: static void exprAnalyze(ExprMaskSet *pMaskSet, ExprInfo *pInfo){
        !           171:   Expr *pExpr = pInfo->p;
        !           172:   pInfo->prereqLeft = exprTableUsage(pMaskSet, pExpr->pLeft);
        !           173:   pInfo->prereqRight = exprTableUsage(pMaskSet, pExpr->pRight);
        !           174:   pInfo->prereqAll = exprTableUsage(pMaskSet, pExpr);
        !           175:   pInfo->indexable = 0;
        !           176:   pInfo->idxLeft = -1;
        !           177:   pInfo->idxRight = -1;
        !           178:   if( allowedOp(pExpr->op) && (pInfo->prereqRight & pInfo->prereqLeft)==0 ){
        !           179:     if( pExpr->pRight && pExpr->pRight->op==TK_COLUMN ){
        !           180:       pInfo->idxRight = pExpr->pRight->iTable;
        !           181:       pInfo->indexable = 1;
        !           182:     }
        !           183:     if( pExpr->pLeft->op==TK_COLUMN ){
        !           184:       pInfo->idxLeft = pExpr->pLeft->iTable;
        !           185:       pInfo->indexable = 1;
        !           186:     }
        !           187:   }
        !           188: }
        !           189: 
        !           190: /*
        !           191: ** pOrderBy is an ORDER BY clause from a SELECT statement.  pTab is the
        !           192: ** left-most table in the FROM clause of that same SELECT statement and
        !           193: ** the table has a cursor number of "base".
        !           194: **
        !           195: ** This routine attempts to find an index for pTab that generates the
        !           196: ** correct record sequence for the given ORDER BY clause.  The return value
        !           197: ** is a pointer to an index that does the job.  NULL is returned if the
        !           198: ** table has no index that will generate the correct sort order.
        !           199: **
        !           200: ** If there are two or more indices that generate the correct sort order
        !           201: ** and pPreferredIdx is one of those indices, then return pPreferredIdx.
        !           202: **
        !           203: ** nEqCol is the number of columns of pPreferredIdx that are used as
        !           204: ** equality constraints.  Any index returned must have exactly this same
        !           205: ** set of columns.  The ORDER BY clause only matches index columns beyond the
        !           206: ** the first nEqCol columns.
        !           207: **
        !           208: ** All terms of the ORDER BY clause must be either ASC or DESC.  The
        !           209: ** *pbRev value is set to 1 if the ORDER BY clause is all DESC and it is
        !           210: ** set to 0 if the ORDER BY clause is all ASC.
        !           211: */
        !           212: static Index *findSortingIndex(
        !           213:   Table *pTab,            /* The table to be sorted */
        !           214:   int base,               /* Cursor number for pTab */
        !           215:   ExprList *pOrderBy,     /* The ORDER BY clause */
        !           216:   Index *pPreferredIdx,   /* Use this index, if possible and not NULL */
        !           217:   int nEqCol,             /* Number of index columns used with == constraints */
        !           218:   int *pbRev              /* Set to 1 if ORDER BY is DESC */
        !           219: ){
        !           220:   int i, j;
        !           221:   Index *pMatch;
        !           222:   Index *pIdx;
        !           223:   int sortOrder;
        !           224: 
        !           225:   assert( pOrderBy!=0 );
        !           226:   assert( pOrderBy->nExpr>0 );
        !           227:   sortOrder = pOrderBy->a[0].sortOrder & SQLITE_SO_DIRMASK;
        !           228:   for(i=0; i<pOrderBy->nExpr; i++){
        !           229:     Expr *p;
        !           230:     if( (pOrderBy->a[i].sortOrder & SQLITE_SO_DIRMASK)!=sortOrder ){
        !           231:       /* Indices can only be used if all ORDER BY terms are either
        !           232:       ** DESC or ASC.  Indices cannot be used on a mixture. */
        !           233:       return 0;
        !           234:     }
        !           235:     if( (pOrderBy->a[i].sortOrder & SQLITE_SO_TYPEMASK)!=SQLITE_SO_UNK ){
        !           236:       /* Do not sort by index if there is a COLLATE clause */
        !           237:       return 0;
        !           238:     }
        !           239:     p = pOrderBy->a[i].pExpr;
        !           240:     if( p->op!=TK_COLUMN || p->iTable!=base ){
        !           241:       /* Can not use an index sort on anything that is not a column in the
        !           242:       ** left-most table of the FROM clause */
        !           243:       return 0;
        !           244:     }
        !           245:   }
        !           246:   
        !           247:   /* If we get this far, it means the ORDER BY clause consists only of
        !           248:   ** ascending columns in the left-most table of the FROM clause.  Now
        !           249:   ** check for a matching index.
        !           250:   */
        !           251:   pMatch = 0;
        !           252:   for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
        !           253:     int nExpr = pOrderBy->nExpr;
        !           254:     if( pIdx->nColumn < nEqCol || pIdx->nColumn < nExpr ) continue;
        !           255:     for(i=j=0; i<nEqCol; i++){
        !           256:       if( pPreferredIdx->aiColumn[i]!=pIdx->aiColumn[i] ) break;
        !           257:       if( j<nExpr && pOrderBy->a[j].pExpr->iColumn==pIdx->aiColumn[i] ){ j++; }
        !           258:     }
        !           259:     if( i<nEqCol ) continue;
        !           260:     for(i=0; i+j<nExpr; i++){
        !           261:       if( pOrderBy->a[i+j].pExpr->iColumn!=pIdx->aiColumn[i+nEqCol] ) break;
        !           262:     }
        !           263:     if( i+j>=nExpr ){
        !           264:       pMatch = pIdx;
        !           265:       if( pIdx==pPreferredIdx ) break;
        !           266:     }
        !           267:   }
        !           268:   if( pMatch && pbRev ){
        !           269:     *pbRev = sortOrder==SQLITE_SO_DESC;
        !           270:   }
        !           271:   return pMatch;
        !           272: }
        !           273: 
        !           274: /*
        !           275: ** Disable a term in the WHERE clause.  Except, do not disable the term
        !           276: ** if it controls a LEFT OUTER JOIN and it did not originate in the ON
        !           277: ** or USING clause of that join.
        !           278: **
        !           279: ** Consider the term t2.z='ok' in the following queries:
        !           280: **
        !           281: **   (1)  SELECT * FROM t1 LEFT JOIN t2 ON t1.a=t2.x WHERE t2.z='ok'
        !           282: **   (2)  SELECT * FROM t1 LEFT JOIN t2 ON t1.a=t2.x AND t2.z='ok'
        !           283: **   (3)  SELECT * FROM t1, t2 WHERE t1.a=t2.x AND t2.z='ok'
        !           284: **
        !           285: ** The t2.z='ok' is disabled in the in (2) because it did not originate
        !           286: ** in the ON clause.  The term is disabled in (3) because it is not part
        !           287: ** of a LEFT OUTER JOIN.  In (1), the term is not disabled.
        !           288: **
        !           289: ** Disabling a term causes that term to not be tested in the inner loop
        !           290: ** of the join.  Disabling is an optimization.  We would get the correct
        !           291: ** results if nothing were ever disabled, but joins might run a little
        !           292: ** slower.  The trick is to disable as much as we can without disabling
        !           293: ** too much.  If we disabled in (1), we'd get the wrong answer.
        !           294: ** See ticket #813.
        !           295: */
        !           296: static void disableTerm(WhereLevel *pLevel, Expr **ppExpr){
        !           297:   Expr *pExpr = *ppExpr;
        !           298:   if( pLevel->iLeftJoin==0 || ExprHasProperty(pExpr, EP_FromJoin) ){
        !           299:     *ppExpr = 0;
        !           300:   }
        !           301: }
        !           302: 
        !           303: /*
        !           304: ** Generate the beginning of the loop used for WHERE clause processing.
        !           305: ** The return value is a pointer to an (opaque) structure that contains
        !           306: ** information needed to terminate the loop.  Later, the calling routine
        !           307: ** should invoke sqliteWhereEnd() with the return value of this function
        !           308: ** in order to complete the WHERE clause processing.
        !           309: **
        !           310: ** If an error occurs, this routine returns NULL.
        !           311: **
        !           312: ** The basic idea is to do a nested loop, one loop for each table in
        !           313: ** the FROM clause of a select.  (INSERT and UPDATE statements are the
        !           314: ** same as a SELECT with only a single table in the FROM clause.)  For
        !           315: ** example, if the SQL is this:
        !           316: **
        !           317: **       SELECT * FROM t1, t2, t3 WHERE ...;
        !           318: **
        !           319: ** Then the code generated is conceptually like the following:
        !           320: **
        !           321: **      foreach row1 in t1 do       \    Code generated
        !           322: **        foreach row2 in t2 do      |-- by sqliteWhereBegin()
        !           323: **          foreach row3 in t3 do   /
        !           324: **            ...
        !           325: **          end                     \    Code generated
        !           326: **        end                        |-- by sqliteWhereEnd()
        !           327: **      end                         /
        !           328: **
        !           329: ** There are Btree cursors associated with each table.  t1 uses cursor
        !           330: ** number pTabList->a[0].iCursor.  t2 uses the cursor pTabList->a[1].iCursor.
        !           331: ** And so forth.  This routine generates code to open those VDBE cursors
        !           332: ** and sqliteWhereEnd() generates the code to close them.
        !           333: **
        !           334: ** If the WHERE clause is empty, the foreach loops must each scan their
        !           335: ** entire tables.  Thus a three-way join is an O(N^3) operation.  But if
        !           336: ** the tables have indices and there are terms in the WHERE clause that
        !           337: ** refer to those indices, a complete table scan can be avoided and the
        !           338: ** code will run much faster.  Most of the work of this routine is checking
        !           339: ** to see if there are indices that can be used to speed up the loop.
        !           340: **
        !           341: ** Terms of the WHERE clause are also used to limit which rows actually
        !           342: ** make it to the "..." in the middle of the loop.  After each "foreach",
        !           343: ** terms of the WHERE clause that use only terms in that loop and outer
        !           344: ** loops are evaluated and if false a jump is made around all subsequent
        !           345: ** inner loops (or around the "..." if the test occurs within the inner-
        !           346: ** most loop)
        !           347: **
        !           348: ** OUTER JOINS
        !           349: **
        !           350: ** An outer join of tables t1 and t2 is conceptally coded as follows:
        !           351: **
        !           352: **    foreach row1 in t1 do
        !           353: **      flag = 0
        !           354: **      foreach row2 in t2 do
        !           355: **        start:
        !           356: **          ...
        !           357: **          flag = 1
        !           358: **      end
        !           359: **      if flag==0 then
        !           360: **        move the row2 cursor to a null row
        !           361: **        goto start
        !           362: **      fi
        !           363: **    end
        !           364: **
        !           365: ** ORDER BY CLAUSE PROCESSING
        !           366: **
        !           367: ** *ppOrderBy is a pointer to the ORDER BY clause of a SELECT statement,
        !           368: ** if there is one.  If there is no ORDER BY clause or if this routine
        !           369: ** is called from an UPDATE or DELETE statement, then ppOrderBy is NULL.
        !           370: **
        !           371: ** If an index can be used so that the natural output order of the table
        !           372: ** scan is correct for the ORDER BY clause, then that index is used and
        !           373: ** *ppOrderBy is set to NULL.  This is an optimization that prevents an
        !           374: ** unnecessary sort of the result set if an index appropriate for the
        !           375: ** ORDER BY clause already exists.
        !           376: **
        !           377: ** If the where clause loops cannot be arranged to provide the correct
        !           378: ** output order, then the *ppOrderBy is unchanged.
        !           379: */
        !           380: WhereInfo *sqliteWhereBegin(
        !           381:   Parse *pParse,       /* The parser context */
        !           382:   SrcList *pTabList,   /* A list of all tables to be scanned */
        !           383:   Expr *pWhere,        /* The WHERE clause */
        !           384:   int pushKey,         /* If TRUE, leave the table key on the stack */
        !           385:   ExprList **ppOrderBy /* An ORDER BY clause, or NULL */
        !           386: ){
        !           387:   int i;                     /* Loop counter */
        !           388:   WhereInfo *pWInfo;         /* Will become the return value of this function */
        !           389:   Vdbe *v = pParse->pVdbe;   /* The virtual database engine */
        !           390:   int brk, cont = 0;         /* Addresses used during code generation */
        !           391:   int nExpr;           /* Number of subexpressions in the WHERE clause */
        !           392:   int loopMask;        /* One bit set for each outer loop */
        !           393:   int haveKey;         /* True if KEY is on the stack */
        !           394:   ExprMaskSet maskSet; /* The expression mask set */
        !           395:   int iDirectEq[32];   /* Term of the form ROWID==X for the N-th table */
        !           396:   int iDirectLt[32];   /* Term of the form ROWID<X or ROWID<=X */
        !           397:   int iDirectGt[32];   /* Term of the form ROWID>X or ROWID>=X */
        !           398:   ExprInfo aExpr[101]; /* The WHERE clause is divided into these expressions */
        !           399: 
        !           400:   /* pushKey is only allowed if there is a single table (as in an INSERT or
        !           401:   ** UPDATE statement)
        !           402:   */
        !           403:   assert( pushKey==0 || pTabList->nSrc==1 );
        !           404: 
        !           405:   /* Split the WHERE clause into separate subexpressions where each
        !           406:   ** subexpression is separated by an AND operator.  If the aExpr[]
        !           407:   ** array fills up, the last entry might point to an expression which
        !           408:   ** contains additional unfactored AND operators.
        !           409:   */
        !           410:   initMaskSet(&maskSet);
        !           411:   memset(aExpr, 0, sizeof(aExpr));
        !           412:   nExpr = exprSplit(ARRAYSIZE(aExpr), aExpr, pWhere);
        !           413:   if( nExpr==ARRAYSIZE(aExpr) ){
        !           414:     sqliteErrorMsg(pParse, "WHERE clause too complex - no more "
        !           415:        "than %d terms allowed", (int)ARRAYSIZE(aExpr)-1);
        !           416:     return 0;
        !           417:   }
        !           418:   
        !           419:   /* Allocate and initialize the WhereInfo structure that will become the
        !           420:   ** return value.
        !           421:   */
        !           422:   pWInfo = sqliteMalloc( sizeof(WhereInfo) + pTabList->nSrc*sizeof(WhereLevel));
        !           423:   if( sqlite_malloc_failed ){
        !           424:     sqliteFree(pWInfo);
        !           425:     return 0;
        !           426:   }
        !           427:   pWInfo->pParse = pParse;
        !           428:   pWInfo->pTabList = pTabList;
        !           429:   pWInfo->peakNTab = pWInfo->savedNTab = pParse->nTab;
        !           430:   pWInfo->iBreak = sqliteVdbeMakeLabel(v);
        !           431: 
        !           432:   /* Special case: a WHERE clause that is constant.  Evaluate the
        !           433:   ** expression and either jump over all of the code or fall thru.
        !           434:   */
        !           435:   if( pWhere && (pTabList->nSrc==0 || sqliteExprIsConstant(pWhere)) ){
        !           436:     sqliteExprIfFalse(pParse, pWhere, pWInfo->iBreak, 1);
        !           437:     pWhere = 0;
        !           438:   }
        !           439: 
        !           440:   /* Analyze all of the subexpressions.
        !           441:   */
        !           442:   for(i=0; i<nExpr; i++){
        !           443:     exprAnalyze(&maskSet, &aExpr[i]);
        !           444: 
        !           445:     /* If we are executing a trigger body, remove all references to
        !           446:     ** new.* and old.* tables from the prerequisite masks.
        !           447:     */
        !           448:     if( pParse->trigStack ){
        !           449:       int x;
        !           450:       if( (x = pParse->trigStack->newIdx) >= 0 ){
        !           451:         int mask = ~getMask(&maskSet, x);
        !           452:         aExpr[i].prereqRight &= mask;
        !           453:         aExpr[i].prereqLeft &= mask;
        !           454:         aExpr[i].prereqAll &= mask;
        !           455:       }
        !           456:       if( (x = pParse->trigStack->oldIdx) >= 0 ){
        !           457:         int mask = ~getMask(&maskSet, x);
        !           458:         aExpr[i].prereqRight &= mask;
        !           459:         aExpr[i].prereqLeft &= mask;
        !           460:         aExpr[i].prereqAll &= mask;
        !           461:       }
        !           462:     }
        !           463:   }
        !           464: 
        !           465:   /* Figure out what index to use (if any) for each nested loop.
        !           466:   ** Make pWInfo->a[i].pIdx point to the index to use for the i-th nested
        !           467:   ** loop where i==0 is the outer loop and i==pTabList->nSrc-1 is the inner
        !           468:   ** loop. 
        !           469:   **
        !           470:   ** If terms exist that use the ROWID of any table, then set the
        !           471:   ** iDirectEq[], iDirectLt[], or iDirectGt[] elements for that table
        !           472:   ** to the index of the term containing the ROWID.  We always prefer
        !           473:   ** to use a ROWID which can directly access a table rather than an
        !           474:   ** index which requires reading an index first to get the rowid then
        !           475:   ** doing a second read of the actual database table.
        !           476:   **
        !           477:   ** Actually, if there are more than 32 tables in the join, only the
        !           478:   ** first 32 tables are candidates for indices.  This is (again) due
        !           479:   ** to the limit of 32 bits in an integer bitmask.
        !           480:   */
        !           481:   loopMask = 0;
        !           482:   for(i=0; i<pTabList->nSrc && i<ARRAYSIZE(iDirectEq); i++){
        !           483:     int j;
        !           484:     int iCur = pTabList->a[i].iCursor;    /* The cursor for this table */
        !           485:     int mask = getMask(&maskSet, iCur);   /* Cursor mask for this table */
        !           486:     Table *pTab = pTabList->a[i].pTab;
        !           487:     Index *pIdx;
        !           488:     Index *pBestIdx = 0;
        !           489:     int bestScore = 0;
        !           490: 
        !           491:     /* Check to see if there is an expression that uses only the
        !           492:     ** ROWID field of this table.  For terms of the form ROWID==expr
        !           493:     ** set iDirectEq[i] to the index of the term.  For terms of the
        !           494:     ** form ROWID<expr or ROWID<=expr set iDirectLt[i] to the term index.
        !           495:     ** For terms like ROWID>expr or ROWID>=expr set iDirectGt[i].
        !           496:     **
        !           497:     ** (Added:) Treat ROWID IN expr like ROWID=expr.
        !           498:     */
        !           499:     pWInfo->a[i].iCur = -1;
        !           500:     iDirectEq[i] = -1;
        !           501:     iDirectLt[i] = -1;
        !           502:     iDirectGt[i] = -1;
        !           503:     for(j=0; j<nExpr; j++){
        !           504:       if( aExpr[j].idxLeft==iCur && aExpr[j].p->pLeft->iColumn<0
        !           505:             && (aExpr[j].prereqRight & loopMask)==aExpr[j].prereqRight ){
        !           506:         switch( aExpr[j].p->op ){
        !           507:           case TK_IN:
        !           508:           case TK_EQ: iDirectEq[i] = j; break;
        !           509:           case TK_LE:
        !           510:           case TK_LT: iDirectLt[i] = j; break;
        !           511:           case TK_GE:
        !           512:           case TK_GT: iDirectGt[i] = j;  break;
        !           513:         }
        !           514:       }
        !           515:       if( aExpr[j].idxRight==iCur && aExpr[j].p->pRight->iColumn<0
        !           516:             && (aExpr[j].prereqLeft & loopMask)==aExpr[j].prereqLeft ){
        !           517:         switch( aExpr[j].p->op ){
        !           518:           case TK_EQ: iDirectEq[i] = j;  break;
        !           519:           case TK_LE:
        !           520:           case TK_LT: iDirectGt[i] = j;  break;
        !           521:           case TK_GE:
        !           522:           case TK_GT: iDirectLt[i] = j;  break;
        !           523:         }
        !           524:       }
        !           525:     }
        !           526:     if( iDirectEq[i]>=0 ){
        !           527:       loopMask |= mask;
        !           528:       pWInfo->a[i].pIdx = 0;
        !           529:       continue;
        !           530:     }
        !           531: 
        !           532:     /* Do a search for usable indices.  Leave pBestIdx pointing to
        !           533:     ** the "best" index.  pBestIdx is left set to NULL if no indices
        !           534:     ** are usable.
        !           535:     **
        !           536:     ** The best index is determined as follows.  For each of the
        !           537:     ** left-most terms that is fixed by an equality operator, add
        !           538:     ** 8 to the score.  The right-most term of the index may be
        !           539:     ** constrained by an inequality.  Add 1 if for an "x<..." constraint
        !           540:     ** and add 2 for an "x>..." constraint.  Chose the index that
        !           541:     ** gives the best score.
        !           542:     **
        !           543:     ** This scoring system is designed so that the score can later be
        !           544:     ** used to determine how the index is used.  If the score&7 is 0
        !           545:     ** then all constraints are equalities.  If score&1 is not 0 then
        !           546:     ** there is an inequality used as a termination key.  (ex: "x<...")
        !           547:     ** If score&2 is not 0 then there is an inequality used as the
        !           548:     ** start key.  (ex: "x>...").  A score or 4 is the special case
        !           549:     ** of an IN operator constraint.  (ex:  "x IN ...").
        !           550:     **
        !           551:     ** The IN operator (as in "<expr> IN (...)") is treated the same as
        !           552:     ** an equality comparison except that it can only be used on the
        !           553:     ** left-most column of an index and other terms of the WHERE clause
        !           554:     ** cannot be used in conjunction with the IN operator to help satisfy
        !           555:     ** other columns of the index.
        !           556:     */
        !           557:     for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
        !           558:       int eqMask = 0;  /* Index columns covered by an x=... term */
        !           559:       int ltMask = 0;  /* Index columns covered by an x<... term */
        !           560:       int gtMask = 0;  /* Index columns covered by an x>... term */
        !           561:       int inMask = 0;  /* Index columns covered by an x IN .. term */
        !           562:       int nEq, m, score;
        !           563: 
        !           564:       if( pIdx->nColumn>32 ) continue;  /* Ignore indices too many columns */
        !           565:       for(j=0; j<nExpr; j++){
        !           566:         if( aExpr[j].idxLeft==iCur 
        !           567:              && (aExpr[j].prereqRight & loopMask)==aExpr[j].prereqRight ){
        !           568:           int iColumn = aExpr[j].p->pLeft->iColumn;
        !           569:           int k;
        !           570:           for(k=0; k<pIdx->nColumn; k++){
        !           571:             if( pIdx->aiColumn[k]==iColumn ){
        !           572:               switch( aExpr[j].p->op ){
        !           573:                 case TK_IN: {
        !           574:                   if( k==0 ) inMask |= 1;
        !           575:                   break;
        !           576:                 }
        !           577:                 case TK_EQ: {
        !           578:                   eqMask |= 1<<k;
        !           579:                   break;
        !           580:                 }
        !           581:                 case TK_LE:
        !           582:                 case TK_LT: {
        !           583:                   ltMask |= 1<<k;
        !           584:                   break;
        !           585:                 }
        !           586:                 case TK_GE:
        !           587:                 case TK_GT: {
        !           588:                   gtMask |= 1<<k;
        !           589:                   break;
        !           590:                 }
        !           591:                 default: {
        !           592:                   /* CANT_HAPPEN */
        !           593:                   assert( 0 );
        !           594:                   break;
        !           595:                 }
        !           596:               }
        !           597:               break;
        !           598:             }
        !           599:           }
        !           600:         }
        !           601:         if( aExpr[j].idxRight==iCur 
        !           602:              && (aExpr[j].prereqLeft & loopMask)==aExpr[j].prereqLeft ){
        !           603:           int iColumn = aExpr[j].p->pRight->iColumn;
        !           604:           int k;
        !           605:           for(k=0; k<pIdx->nColumn; k++){
        !           606:             if( pIdx->aiColumn[k]==iColumn ){
        !           607:               switch( aExpr[j].p->op ){
        !           608:                 case TK_EQ: {
        !           609:                   eqMask |= 1<<k;
        !           610:                   break;
        !           611:                 }
        !           612:                 case TK_LE:
        !           613:                 case TK_LT: {
        !           614:                   gtMask |= 1<<k;
        !           615:                   break;
        !           616:                 }
        !           617:                 case TK_GE:
        !           618:                 case TK_GT: {
        !           619:                   ltMask |= 1<<k;
        !           620:                   break;
        !           621:                 }
        !           622:                 default: {
        !           623:                   /* CANT_HAPPEN */
        !           624:                   assert( 0 );
        !           625:                   break;
        !           626:                 }
        !           627:               }
        !           628:               break;
        !           629:             }
        !           630:           }
        !           631:         }
        !           632:       }
        !           633: 
        !           634:       /* The following loop ends with nEq set to the number of columns
        !           635:       ** on the left of the index with == constraints.
        !           636:       */
        !           637:       for(nEq=0; nEq<pIdx->nColumn; nEq++){
        !           638:         m = (1<<(nEq+1))-1;
        !           639:         if( (m & eqMask)!=m ) break;
        !           640:       }
        !           641:       score = nEq*8;   /* Base score is 8 times number of == constraints */
        !           642:       m = 1<<nEq;
        !           643:       if( m & ltMask ) score++;    /* Increase score for a < constraint */
        !           644:       if( m & gtMask ) score+=2;   /* Increase score for a > constraint */
        !           645:       if( score==0 && inMask ) score = 4;  /* Default score for IN constraint */
        !           646:       if( score>bestScore ){
        !           647:         pBestIdx = pIdx;
        !           648:         bestScore = score;
        !           649:       }
        !           650:     }
        !           651:     pWInfo->a[i].pIdx = pBestIdx;
        !           652:     pWInfo->a[i].score = bestScore;
        !           653:     pWInfo->a[i].bRev = 0;
        !           654:     loopMask |= mask;
        !           655:     if( pBestIdx ){
        !           656:       pWInfo->a[i].iCur = pParse->nTab++;
        !           657:       pWInfo->peakNTab = pParse->nTab;
        !           658:     }
        !           659:   }
        !           660: 
        !           661:   /* Check to see if the ORDER BY clause is or can be satisfied by the
        !           662:   ** use of an index on the first table.
        !           663:   */
        !           664:   if( ppOrderBy && *ppOrderBy && pTabList->nSrc>0 ){
        !           665:      Index *pSortIdx;
        !           666:      Index *pIdx;
        !           667:      Table *pTab;
        !           668:      int bRev = 0;
        !           669: 
        !           670:      pTab = pTabList->a[0].pTab;
        !           671:      pIdx = pWInfo->a[0].pIdx;
        !           672:      if( pIdx && pWInfo->a[0].score==4 ){
        !           673:        /* If there is already an IN index on the left-most table,
        !           674:        ** it will not give the correct sort order.
        !           675:        ** So, pretend that no suitable index is found.
        !           676:        */
        !           677:        pSortIdx = 0;
        !           678:      }else if( iDirectEq[0]>=0 || iDirectLt[0]>=0 || iDirectGt[0]>=0 ){
        !           679:        /* If the left-most column is accessed using its ROWID, then do
        !           680:        ** not try to sort by index.
        !           681:        */
        !           682:        pSortIdx = 0;
        !           683:      }else{
        !           684:        int nEqCol = (pWInfo->a[0].score+4)/8;
        !           685:        pSortIdx = findSortingIndex(pTab, pTabList->a[0].iCursor, 
        !           686:                                    *ppOrderBy, pIdx, nEqCol, &bRev);
        !           687:      }
        !           688:      if( pSortIdx && (pIdx==0 || pIdx==pSortIdx) ){
        !           689:        if( pIdx==0 ){
        !           690:          pWInfo->a[0].pIdx = pSortIdx;
        !           691:          pWInfo->a[0].iCur = pParse->nTab++;
        !           692:          pWInfo->peakNTab = pParse->nTab;
        !           693:        }
        !           694:        pWInfo->a[0].bRev = bRev;
        !           695:        *ppOrderBy = 0;
        !           696:      }
        !           697:   }
        !           698: 
        !           699:   /* Open all tables in the pTabList and all indices used by those tables.
        !           700:   */
        !           701:   for(i=0; i<pTabList->nSrc; i++){
        !           702:     Table *pTab;
        !           703:     Index *pIx;
        !           704: 
        !           705:     pTab = pTabList->a[i].pTab;
        !           706:     if( pTab->isTransient || pTab->pSelect ) continue;
        !           707:     sqliteVdbeAddOp(v, OP_Integer, pTab->iDb, 0);
        !           708:     sqliteVdbeOp3(v, OP_OpenRead, pTabList->a[i].iCursor, pTab->tnum,
        !           709:                      pTab->zName, P3_STATIC);
        !           710:     sqliteCodeVerifySchema(pParse, pTab->iDb);
        !           711:     if( (pIx = pWInfo->a[i].pIdx)!=0 ){
        !           712:       sqliteVdbeAddOp(v, OP_Integer, pIx->iDb, 0);
        !           713:       sqliteVdbeOp3(v, OP_OpenRead, pWInfo->a[i].iCur, pIx->tnum, pIx->zName,0);
        !           714:     }
        !           715:   }
        !           716: 
        !           717:   /* Generate the code to do the search
        !           718:   */
        !           719:   loopMask = 0;
        !           720:   for(i=0; i<pTabList->nSrc; i++){
        !           721:     int j, k;
        !           722:     int iCur = pTabList->a[i].iCursor;
        !           723:     Index *pIdx;
        !           724:     WhereLevel *pLevel = &pWInfo->a[i];
        !           725: 
        !           726:     /* If this is the right table of a LEFT OUTER JOIN, allocate and
        !           727:     ** initialize a memory cell that records if this table matches any
        !           728:     ** row of the left table of the join.
        !           729:     */
        !           730:     if( i>0 && (pTabList->a[i-1].jointype & JT_LEFT)!=0 ){
        !           731:       if( !pParse->nMem ) pParse->nMem++;
        !           732:       pLevel->iLeftJoin = pParse->nMem++;
        !           733:       sqliteVdbeAddOp(v, OP_String, 0, 0);
        !           734:       sqliteVdbeAddOp(v, OP_MemStore, pLevel->iLeftJoin, 1);
        !           735:     }
        !           736: 
        !           737:     pIdx = pLevel->pIdx;
        !           738:     pLevel->inOp = OP_Noop;
        !           739:     if( i<ARRAYSIZE(iDirectEq) && iDirectEq[i]>=0 ){
        !           740:       /* Case 1:  We can directly reference a single row using an
        !           741:       **          equality comparison against the ROWID field.  Or
        !           742:       **          we reference multiple rows using a "rowid IN (...)"
        !           743:       **          construct.
        !           744:       */
        !           745:       k = iDirectEq[i];
        !           746:       assert( k<nExpr );
        !           747:       assert( aExpr[k].p!=0 );
        !           748:       assert( aExpr[k].idxLeft==iCur || aExpr[k].idxRight==iCur );
        !           749:       brk = pLevel->brk = sqliteVdbeMakeLabel(v);
        !           750:       if( aExpr[k].idxLeft==iCur ){
        !           751:         Expr *pX = aExpr[k].p;
        !           752:         if( pX->op!=TK_IN ){
        !           753:           sqliteExprCode(pParse, aExpr[k].p->pRight);
        !           754:         }else if( pX->pList ){
        !           755:           sqliteVdbeAddOp(v, OP_SetFirst, pX->iTable, brk);
        !           756:           pLevel->inOp = OP_SetNext;
        !           757:           pLevel->inP1 = pX->iTable;
        !           758:           pLevel->inP2 = sqliteVdbeCurrentAddr(v);
        !           759:         }else{
        !           760:           assert( pX->pSelect );
        !           761:           sqliteVdbeAddOp(v, OP_Rewind, pX->iTable, brk);
        !           762:           sqliteVdbeAddOp(v, OP_KeyAsData, pX->iTable, 1);
        !           763:           pLevel->inP2 = sqliteVdbeAddOp(v, OP_FullKey, pX->iTable, 0);
        !           764:           pLevel->inOp = OP_Next;
        !           765:           pLevel->inP1 = pX->iTable;
        !           766:         }
        !           767:       }else{
        !           768:         sqliteExprCode(pParse, aExpr[k].p->pLeft);
        !           769:       }
        !           770:       disableTerm(pLevel, &aExpr[k].p);
        !           771:       cont = pLevel->cont = sqliteVdbeMakeLabel(v);
        !           772:       sqliteVdbeAddOp(v, OP_MustBeInt, 1, brk);
        !           773:       haveKey = 0;
        !           774:       sqliteVdbeAddOp(v, OP_NotExists, iCur, brk);
        !           775:       pLevel->op = OP_Noop;
        !           776:     }else if( pIdx!=0 && pLevel->score>0 && pLevel->score%4==0 ){
        !           777:       /* Case 2:  There is an index and all terms of the WHERE clause that
        !           778:       **          refer to the index use the "==" or "IN" operators.
        !           779:       */
        !           780:       int start;
        !           781:       int testOp;
        !           782:       int nColumn = (pLevel->score+4)/8;
        !           783:       brk = pLevel->brk = sqliteVdbeMakeLabel(v);
        !           784:       for(j=0; j<nColumn; j++){
        !           785:         for(k=0; k<nExpr; k++){
        !           786:           Expr *pX = aExpr[k].p;
        !           787:           if( pX==0 ) continue;
        !           788:           if( aExpr[k].idxLeft==iCur
        !           789:              && (aExpr[k].prereqRight & loopMask)==aExpr[k].prereqRight 
        !           790:              && pX->pLeft->iColumn==pIdx->aiColumn[j]
        !           791:           ){
        !           792:             if( pX->op==TK_EQ ){
        !           793:               sqliteExprCode(pParse, pX->pRight);
        !           794:               disableTerm(pLevel, &aExpr[k].p);
        !           795:               break;
        !           796:             }
        !           797:             if( pX->op==TK_IN && nColumn==1 ){
        !           798:               if( pX->pList ){
        !           799:                 sqliteVdbeAddOp(v, OP_SetFirst, pX->iTable, brk);
        !           800:                 pLevel->inOp = OP_SetNext;
        !           801:                 pLevel->inP1 = pX->iTable;
        !           802:                 pLevel->inP2 = sqliteVdbeCurrentAddr(v);
        !           803:               }else{
        !           804:                 assert( pX->pSelect );
        !           805:                 sqliteVdbeAddOp(v, OP_Rewind, pX->iTable, brk);
        !           806:                 sqliteVdbeAddOp(v, OP_KeyAsData, pX->iTable, 1);
        !           807:                 pLevel->inP2 = sqliteVdbeAddOp(v, OP_FullKey, pX->iTable, 0);
        !           808:                 pLevel->inOp = OP_Next;
        !           809:                 pLevel->inP1 = pX->iTable;
        !           810:               }
        !           811:               disableTerm(pLevel, &aExpr[k].p);
        !           812:               break;
        !           813:             }
        !           814:           }
        !           815:           if( aExpr[k].idxRight==iCur
        !           816:              && aExpr[k].p->op==TK_EQ
        !           817:              && (aExpr[k].prereqLeft & loopMask)==aExpr[k].prereqLeft
        !           818:              && aExpr[k].p->pRight->iColumn==pIdx->aiColumn[j]
        !           819:           ){
        !           820:             sqliteExprCode(pParse, aExpr[k].p->pLeft);
        !           821:             disableTerm(pLevel, &aExpr[k].p);
        !           822:             break;
        !           823:           }
        !           824:         }
        !           825:       }
        !           826:       pLevel->iMem = pParse->nMem++;
        !           827:       cont = pLevel->cont = sqliteVdbeMakeLabel(v);
        !           828:       sqliteVdbeAddOp(v, OP_NotNull, -nColumn, sqliteVdbeCurrentAddr(v)+3);
        !           829:       sqliteVdbeAddOp(v, OP_Pop, nColumn, 0);
        !           830:       sqliteVdbeAddOp(v, OP_Goto, 0, brk);
        !           831:       sqliteVdbeAddOp(v, OP_MakeKey, nColumn, 0);
        !           832:       sqliteAddIdxKeyType(v, pIdx);
        !           833:       if( nColumn==pIdx->nColumn || pLevel->bRev ){
        !           834:         sqliteVdbeAddOp(v, OP_MemStore, pLevel->iMem, 0);
        !           835:         testOp = OP_IdxGT;
        !           836:       }else{
        !           837:         sqliteVdbeAddOp(v, OP_Dup, 0, 0);
        !           838:         sqliteVdbeAddOp(v, OP_IncrKey, 0, 0);
        !           839:         sqliteVdbeAddOp(v, OP_MemStore, pLevel->iMem, 1);
        !           840:         testOp = OP_IdxGE;
        !           841:       }
        !           842:       if( pLevel->bRev ){
        !           843:         /* Scan in reverse order */
        !           844:         sqliteVdbeAddOp(v, OP_IncrKey, 0, 0);
        !           845:         sqliteVdbeAddOp(v, OP_MoveLt, pLevel->iCur, brk);
        !           846:         start = sqliteVdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
        !           847:         sqliteVdbeAddOp(v, OP_IdxLT, pLevel->iCur, brk);
        !           848:         pLevel->op = OP_Prev;
        !           849:       }else{
        !           850:         /* Scan in the forward order */
        !           851:         sqliteVdbeAddOp(v, OP_MoveTo, pLevel->iCur, brk);
        !           852:         start = sqliteVdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
        !           853:         sqliteVdbeAddOp(v, testOp, pLevel->iCur, brk);
        !           854:         pLevel->op = OP_Next;
        !           855:       }
        !           856:       sqliteVdbeAddOp(v, OP_RowKey, pLevel->iCur, 0);
        !           857:       sqliteVdbeAddOp(v, OP_IdxIsNull, nColumn, cont);
        !           858:       sqliteVdbeAddOp(v, OP_IdxRecno, pLevel->iCur, 0);
        !           859:       if( i==pTabList->nSrc-1 && pushKey ){
        !           860:         haveKey = 1;
        !           861:       }else{
        !           862:         sqliteVdbeAddOp(v, OP_MoveTo, iCur, 0);
        !           863:         haveKey = 0;
        !           864:       }
        !           865:       pLevel->p1 = pLevel->iCur;
        !           866:       pLevel->p2 = start;
        !           867:     }else if( i<ARRAYSIZE(iDirectLt) && (iDirectLt[i]>=0 || iDirectGt[i]>=0) ){
        !           868:       /* Case 3:  We have an inequality comparison against the ROWID field.
        !           869:       */
        !           870:       int testOp = OP_Noop;
        !           871:       int start;
        !           872: 
        !           873:       brk = pLevel->brk = sqliteVdbeMakeLabel(v);
        !           874:       cont = pLevel->cont = sqliteVdbeMakeLabel(v);
        !           875:       if( iDirectGt[i]>=0 ){
        !           876:         k = iDirectGt[i];
        !           877:         assert( k<nExpr );
        !           878:         assert( aExpr[k].p!=0 );
        !           879:         assert( aExpr[k].idxLeft==iCur || aExpr[k].idxRight==iCur );
        !           880:         if( aExpr[k].idxLeft==iCur ){
        !           881:           sqliteExprCode(pParse, aExpr[k].p->pRight);
        !           882:         }else{
        !           883:           sqliteExprCode(pParse, aExpr[k].p->pLeft);
        !           884:         }
        !           885:         sqliteVdbeAddOp(v, OP_ForceInt,
        !           886:           aExpr[k].p->op==TK_LT || aExpr[k].p->op==TK_GT, brk);
        !           887:         sqliteVdbeAddOp(v, OP_MoveTo, iCur, brk);
        !           888:         disableTerm(pLevel, &aExpr[k].p);
        !           889:       }else{
        !           890:         sqliteVdbeAddOp(v, OP_Rewind, iCur, brk);
        !           891:       }
        !           892:       if( iDirectLt[i]>=0 ){
        !           893:         k = iDirectLt[i];
        !           894:         assert( k<nExpr );
        !           895:         assert( aExpr[k].p!=0 );
        !           896:         assert( aExpr[k].idxLeft==iCur || aExpr[k].idxRight==iCur );
        !           897:         if( aExpr[k].idxLeft==iCur ){
        !           898:           sqliteExprCode(pParse, aExpr[k].p->pRight);
        !           899:         }else{
        !           900:           sqliteExprCode(pParse, aExpr[k].p->pLeft);
        !           901:         }
        !           902:         /* sqliteVdbeAddOp(v, OP_MustBeInt, 0, sqliteVdbeCurrentAddr(v)+1); */
        !           903:         pLevel->iMem = pParse->nMem++;
        !           904:         sqliteVdbeAddOp(v, OP_MemStore, pLevel->iMem, 1);
        !           905:         if( aExpr[k].p->op==TK_LT || aExpr[k].p->op==TK_GT ){
        !           906:           testOp = OP_Ge;
        !           907:         }else{
        !           908:           testOp = OP_Gt;
        !           909:         }
        !           910:         disableTerm(pLevel, &aExpr[k].p);
        !           911:       }
        !           912:       start = sqliteVdbeCurrentAddr(v);
        !           913:       pLevel->op = OP_Next;
        !           914:       pLevel->p1 = iCur;
        !           915:       pLevel->p2 = start;
        !           916:       if( testOp!=OP_Noop ){
        !           917:         sqliteVdbeAddOp(v, OP_Recno, iCur, 0);
        !           918:         sqliteVdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
        !           919:         sqliteVdbeAddOp(v, testOp, 0, brk);
        !           920:       }
        !           921:       haveKey = 0;
        !           922:     }else if( pIdx==0 ){
        !           923:       /* Case 4:  There is no usable index.  We must do a complete
        !           924:       **          scan of the entire database table.
        !           925:       */
        !           926:       int start;
        !           927: 
        !           928:       brk = pLevel->brk = sqliteVdbeMakeLabel(v);
        !           929:       cont = pLevel->cont = sqliteVdbeMakeLabel(v);
        !           930:       sqliteVdbeAddOp(v, OP_Rewind, iCur, brk);
        !           931:       start = sqliteVdbeCurrentAddr(v);
        !           932:       pLevel->op = OP_Next;
        !           933:       pLevel->p1 = iCur;
        !           934:       pLevel->p2 = start;
        !           935:       haveKey = 0;
        !           936:     }else{
        !           937:       /* Case 5: The WHERE clause term that refers to the right-most
        !           938:       **         column of the index is an inequality.  For example, if
        !           939:       **         the index is on (x,y,z) and the WHERE clause is of the
        !           940:       **         form "x=5 AND y<10" then this case is used.  Only the
        !           941:       **         right-most column can be an inequality - the rest must
        !           942:       **         use the "==" operator.
        !           943:       **
        !           944:       **         This case is also used when there are no WHERE clause
        !           945:       **         constraints but an index is selected anyway, in order
        !           946:       **         to force the output order to conform to an ORDER BY.
        !           947:       */
        !           948:       int score = pLevel->score;
        !           949:       int nEqColumn = score/8;
        !           950:       int start;
        !           951:       int leFlag, geFlag;
        !           952:       int testOp;
        !           953: 
        !           954:       /* Evaluate the equality constraints
        !           955:       */
        !           956:       for(j=0; j<nEqColumn; j++){
        !           957:         for(k=0; k<nExpr; k++){
        !           958:           if( aExpr[k].p==0 ) continue;
        !           959:           if( aExpr[k].idxLeft==iCur
        !           960:              && aExpr[k].p->op==TK_EQ
        !           961:              && (aExpr[k].prereqRight & loopMask)==aExpr[k].prereqRight 
        !           962:              && aExpr[k].p->pLeft->iColumn==pIdx->aiColumn[j]
        !           963:           ){
        !           964:             sqliteExprCode(pParse, aExpr[k].p->pRight);
        !           965:             disableTerm(pLevel, &aExpr[k].p);
        !           966:             break;
        !           967:           }
        !           968:           if( aExpr[k].idxRight==iCur
        !           969:              && aExpr[k].p->op==TK_EQ
        !           970:              && (aExpr[k].prereqLeft & loopMask)==aExpr[k].prereqLeft
        !           971:              && aExpr[k].p->pRight->iColumn==pIdx->aiColumn[j]
        !           972:           ){
        !           973:             sqliteExprCode(pParse, aExpr[k].p->pLeft);
        !           974:             disableTerm(pLevel, &aExpr[k].p);
        !           975:             break;
        !           976:           }
        !           977:         }
        !           978:       }
        !           979: 
        !           980:       /* Duplicate the equality term values because they will all be
        !           981:       ** used twice: once to make the termination key and once to make the
        !           982:       ** start key.
        !           983:       */
        !           984:       for(j=0; j<nEqColumn; j++){
        !           985:         sqliteVdbeAddOp(v, OP_Dup, nEqColumn-1, 0);
        !           986:       }
        !           987: 
        !           988:       /* Labels for the beginning and end of the loop
        !           989:       */
        !           990:       cont = pLevel->cont = sqliteVdbeMakeLabel(v);
        !           991:       brk = pLevel->brk = sqliteVdbeMakeLabel(v);
        !           992: 
        !           993:       /* Generate the termination key.  This is the key value that
        !           994:       ** will end the search.  There is no termination key if there
        !           995:       ** are no equality terms and no "X<..." term.
        !           996:       **
        !           997:       ** 2002-Dec-04: On a reverse-order scan, the so-called "termination"
        !           998:       ** key computed here really ends up being the start key.
        !           999:       */
        !          1000:       if( (score & 1)!=0 ){
        !          1001:         for(k=0; k<nExpr; k++){
        !          1002:           Expr *pExpr = aExpr[k].p;
        !          1003:           if( pExpr==0 ) continue;
        !          1004:           if( aExpr[k].idxLeft==iCur
        !          1005:              && (pExpr->op==TK_LT || pExpr->op==TK_LE)
        !          1006:              && (aExpr[k].prereqRight & loopMask)==aExpr[k].prereqRight 
        !          1007:              && pExpr->pLeft->iColumn==pIdx->aiColumn[j]
        !          1008:           ){
        !          1009:             sqliteExprCode(pParse, pExpr->pRight);
        !          1010:             leFlag = pExpr->op==TK_LE;
        !          1011:             disableTerm(pLevel, &aExpr[k].p);
        !          1012:             break;
        !          1013:           }
        !          1014:           if( aExpr[k].idxRight==iCur
        !          1015:              && (pExpr->op==TK_GT || pExpr->op==TK_GE)
        !          1016:              && (aExpr[k].prereqLeft & loopMask)==aExpr[k].prereqLeft
        !          1017:              && pExpr->pRight->iColumn==pIdx->aiColumn[j]
        !          1018:           ){
        !          1019:             sqliteExprCode(pParse, pExpr->pLeft);
        !          1020:             leFlag = pExpr->op==TK_GE;
        !          1021:             disableTerm(pLevel, &aExpr[k].p);
        !          1022:             break;
        !          1023:           }
        !          1024:         }
        !          1025:         testOp = OP_IdxGE;
        !          1026:       }else{
        !          1027:         testOp = nEqColumn>0 ? OP_IdxGE : OP_Noop;
        !          1028:         leFlag = 1;
        !          1029:       }
        !          1030:       if( testOp!=OP_Noop ){
        !          1031:         int nCol = nEqColumn + (score & 1);
        !          1032:         pLevel->iMem = pParse->nMem++;
        !          1033:         sqliteVdbeAddOp(v, OP_NotNull, -nCol, sqliteVdbeCurrentAddr(v)+3);
        !          1034:         sqliteVdbeAddOp(v, OP_Pop, nCol, 0);
        !          1035:         sqliteVdbeAddOp(v, OP_Goto, 0, brk);
        !          1036:         sqliteVdbeAddOp(v, OP_MakeKey, nCol, 0);
        !          1037:         sqliteAddIdxKeyType(v, pIdx);
        !          1038:         if( leFlag ){
        !          1039:           sqliteVdbeAddOp(v, OP_IncrKey, 0, 0);
        !          1040:         }
        !          1041:         if( pLevel->bRev ){
        !          1042:           sqliteVdbeAddOp(v, OP_MoveLt, pLevel->iCur, brk);
        !          1043:         }else{
        !          1044:           sqliteVdbeAddOp(v, OP_MemStore, pLevel->iMem, 1);
        !          1045:         }
        !          1046:       }else if( pLevel->bRev ){
        !          1047:         sqliteVdbeAddOp(v, OP_Last, pLevel->iCur, brk);
        !          1048:       }
        !          1049: 
        !          1050:       /* Generate the start key.  This is the key that defines the lower
        !          1051:       ** bound on the search.  There is no start key if there are no
        !          1052:       ** equality terms and if there is no "X>..." term.  In
        !          1053:       ** that case, generate a "Rewind" instruction in place of the
        !          1054:       ** start key search.
        !          1055:       **
        !          1056:       ** 2002-Dec-04: In the case of a reverse-order search, the so-called
        !          1057:       ** "start" key really ends up being used as the termination key.
        !          1058:       */
        !          1059:       if( (score & 2)!=0 ){
        !          1060:         for(k=0; k<nExpr; k++){
        !          1061:           Expr *pExpr = aExpr[k].p;
        !          1062:           if( pExpr==0 ) continue;
        !          1063:           if( aExpr[k].idxLeft==iCur
        !          1064:              && (pExpr->op==TK_GT || pExpr->op==TK_GE)
        !          1065:              && (aExpr[k].prereqRight & loopMask)==aExpr[k].prereqRight 
        !          1066:              && pExpr->pLeft->iColumn==pIdx->aiColumn[j]
        !          1067:           ){
        !          1068:             sqliteExprCode(pParse, pExpr->pRight);
        !          1069:             geFlag = pExpr->op==TK_GE;
        !          1070:             disableTerm(pLevel, &aExpr[k].p);
        !          1071:             break;
        !          1072:           }
        !          1073:           if( aExpr[k].idxRight==iCur
        !          1074:              && (pExpr->op==TK_LT || pExpr->op==TK_LE)
        !          1075:              && (aExpr[k].prereqLeft & loopMask)==aExpr[k].prereqLeft
        !          1076:              && pExpr->pRight->iColumn==pIdx->aiColumn[j]
        !          1077:           ){
        !          1078:             sqliteExprCode(pParse, pExpr->pLeft);
        !          1079:             geFlag = pExpr->op==TK_LE;
        !          1080:             disableTerm(pLevel, &aExpr[k].p);
        !          1081:             break;
        !          1082:           }
        !          1083:         }
        !          1084:       }else{
        !          1085:         geFlag = 1;
        !          1086:       }
        !          1087:       if( nEqColumn>0 || (score&2)!=0 ){
        !          1088:         int nCol = nEqColumn + ((score&2)!=0);
        !          1089:         sqliteVdbeAddOp(v, OP_NotNull, -nCol, sqliteVdbeCurrentAddr(v)+3);
        !          1090:         sqliteVdbeAddOp(v, OP_Pop, nCol, 0);
        !          1091:         sqliteVdbeAddOp(v, OP_Goto, 0, brk);
        !          1092:         sqliteVdbeAddOp(v, OP_MakeKey, nCol, 0);
        !          1093:         sqliteAddIdxKeyType(v, pIdx);
        !          1094:         if( !geFlag ){
        !          1095:           sqliteVdbeAddOp(v, OP_IncrKey, 0, 0);
        !          1096:         }
        !          1097:         if( pLevel->bRev ){
        !          1098:           pLevel->iMem = pParse->nMem++;
        !          1099:           sqliteVdbeAddOp(v, OP_MemStore, pLevel->iMem, 1);
        !          1100:           testOp = OP_IdxLT;
        !          1101:         }else{
        !          1102:           sqliteVdbeAddOp(v, OP_MoveTo, pLevel->iCur, brk);
        !          1103:         }
        !          1104:       }else if( pLevel->bRev ){
        !          1105:         testOp = OP_Noop;
        !          1106:       }else{
        !          1107:         sqliteVdbeAddOp(v, OP_Rewind, pLevel->iCur, brk);
        !          1108:       }
        !          1109: 
        !          1110:       /* Generate the the top of the loop.  If there is a termination
        !          1111:       ** key we have to test for that key and abort at the top of the
        !          1112:       ** loop.
        !          1113:       */
        !          1114:       start = sqliteVdbeCurrentAddr(v);
        !          1115:       if( testOp!=OP_Noop ){
        !          1116:         sqliteVdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
        !          1117:         sqliteVdbeAddOp(v, testOp, pLevel->iCur, brk);
        !          1118:       }
        !          1119:       sqliteVdbeAddOp(v, OP_RowKey, pLevel->iCur, 0);
        !          1120:       sqliteVdbeAddOp(v, OP_IdxIsNull, nEqColumn + (score & 1), cont);
        !          1121:       sqliteVdbeAddOp(v, OP_IdxRecno, pLevel->iCur, 0);
        !          1122:       if( i==pTabList->nSrc-1 && pushKey ){
        !          1123:         haveKey = 1;
        !          1124:       }else{
        !          1125:         sqliteVdbeAddOp(v, OP_MoveTo, iCur, 0);
        !          1126:         haveKey = 0;
        !          1127:       }
        !          1128: 
        !          1129:       /* Record the instruction used to terminate the loop.
        !          1130:       */
        !          1131:       pLevel->op = pLevel->bRev ? OP_Prev : OP_Next;
        !          1132:       pLevel->p1 = pLevel->iCur;
        !          1133:       pLevel->p2 = start;
        !          1134:     }
        !          1135:     loopMask |= getMask(&maskSet, iCur);
        !          1136: 
        !          1137:     /* Insert code to test every subexpression that can be completely
        !          1138:     ** computed using the current set of tables.
        !          1139:     */
        !          1140:     for(j=0; j<nExpr; j++){
        !          1141:       if( aExpr[j].p==0 ) continue;
        !          1142:       if( (aExpr[j].prereqAll & loopMask)!=aExpr[j].prereqAll ) continue;
        !          1143:       if( pLevel->iLeftJoin && !ExprHasProperty(aExpr[j].p,EP_FromJoin) ){
        !          1144:         continue;
        !          1145:       }
        !          1146:       if( haveKey ){
        !          1147:         haveKey = 0;
        !          1148:         sqliteVdbeAddOp(v, OP_MoveTo, iCur, 0);
        !          1149:       }
        !          1150:       sqliteExprIfFalse(pParse, aExpr[j].p, cont, 1);
        !          1151:       aExpr[j].p = 0;
        !          1152:     }
        !          1153:     brk = cont;
        !          1154: 
        !          1155:     /* For a LEFT OUTER JOIN, generate code that will record the fact that
        !          1156:     ** at least one row of the right table has matched the left table.  
        !          1157:     */
        !          1158:     if( pLevel->iLeftJoin ){
        !          1159:       pLevel->top = sqliteVdbeCurrentAddr(v);
        !          1160:       sqliteVdbeAddOp(v, OP_Integer, 1, 0);
        !          1161:       sqliteVdbeAddOp(v, OP_MemStore, pLevel->iLeftJoin, 1);
        !          1162:       for(j=0; j<nExpr; j++){
        !          1163:         if( aExpr[j].p==0 ) continue;
        !          1164:         if( (aExpr[j].prereqAll & loopMask)!=aExpr[j].prereqAll ) continue;
        !          1165:         if( haveKey ){
        !          1166:           /* Cannot happen.  "haveKey" can only be true if pushKey is true
        !          1167:           ** an pushKey can only be true for DELETE and UPDATE and there are
        !          1168:           ** no outer joins with DELETE and UPDATE.
        !          1169:           */
        !          1170:           haveKey = 0;
        !          1171:           sqliteVdbeAddOp(v, OP_MoveTo, iCur, 0);
        !          1172:         }
        !          1173:         sqliteExprIfFalse(pParse, aExpr[j].p, cont, 1);
        !          1174:         aExpr[j].p = 0;
        !          1175:       }
        !          1176:     }
        !          1177:   }
        !          1178:   pWInfo->iContinue = cont;
        !          1179:   if( pushKey && !haveKey ){
        !          1180:     sqliteVdbeAddOp(v, OP_Recno, pTabList->a[0].iCursor, 0);
        !          1181:   }
        !          1182:   freeMaskSet(&maskSet);
        !          1183:   return pWInfo;
        !          1184: }
        !          1185: 
        !          1186: /*
        !          1187: ** Generate the end of the WHERE loop.  See comments on 
        !          1188: ** sqliteWhereBegin() for additional information.
        !          1189: */
        !          1190: void sqliteWhereEnd(WhereInfo *pWInfo){
        !          1191:   Vdbe *v = pWInfo->pParse->pVdbe;
        !          1192:   int i;
        !          1193:   WhereLevel *pLevel;
        !          1194:   SrcList *pTabList = pWInfo->pTabList;
        !          1195: 
        !          1196:   for(i=pTabList->nSrc-1; i>=0; i--){
        !          1197:     pLevel = &pWInfo->a[i];
        !          1198:     sqliteVdbeResolveLabel(v, pLevel->cont);
        !          1199:     if( pLevel->op!=OP_Noop ){
        !          1200:       sqliteVdbeAddOp(v, pLevel->op, pLevel->p1, pLevel->p2);
        !          1201:     }
        !          1202:     sqliteVdbeResolveLabel(v, pLevel->brk);
        !          1203:     if( pLevel->inOp!=OP_Noop ){
        !          1204:       sqliteVdbeAddOp(v, pLevel->inOp, pLevel->inP1, pLevel->inP2);
        !          1205:     }
        !          1206:     if( pLevel->iLeftJoin ){
        !          1207:       int addr;
        !          1208:       addr = sqliteVdbeAddOp(v, OP_MemLoad, pLevel->iLeftJoin, 0);
        !          1209:       sqliteVdbeAddOp(v, OP_NotNull, 1, addr+4 + (pLevel->iCur>=0));
        !          1210:       sqliteVdbeAddOp(v, OP_NullRow, pTabList->a[i].iCursor, 0);
        !          1211:       if( pLevel->iCur>=0 ){
        !          1212:         sqliteVdbeAddOp(v, OP_NullRow, pLevel->iCur, 0);
        !          1213:       }
        !          1214:       sqliteVdbeAddOp(v, OP_Goto, 0, pLevel->top);
        !          1215:     }
        !          1216:   }
        !          1217:   sqliteVdbeResolveLabel(v, pWInfo->iBreak);
        !          1218:   for(i=0; i<pTabList->nSrc; i++){
        !          1219:     Table *pTab = pTabList->a[i].pTab;
        !          1220:     assert( pTab!=0 );
        !          1221:     if( pTab->isTransient || pTab->pSelect ) continue;
        !          1222:     pLevel = &pWInfo->a[i];
        !          1223:     sqliteVdbeAddOp(v, OP_Close, pTabList->a[i].iCursor, 0);
        !          1224:     if( pLevel->pIdx!=0 ){
        !          1225:       sqliteVdbeAddOp(v, OP_Close, pLevel->iCur, 0);
        !          1226:     }
        !          1227:   }
        !          1228: #if 0  /* Never reuse a cursor */
        !          1229:   if( pWInfo->pParse->nTab==pWInfo->peakNTab ){
        !          1230:     pWInfo->pParse->nTab = pWInfo->savedNTab;
        !          1231:   }
        !          1232: #endif
        !          1233:   sqliteFree(pWInfo);
        !          1234:   return;
        !          1235: }

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