Annotation of embedaddon/php/ext/sqlite/libsqlite/src/where.c, revision 1.1.1.1

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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