xref: /illumos-gate/usr/src/lib/libsqlite/src/where.c (revision 1da57d551424de5a9d469760be7c4b4d4f10a755)
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,v 1.89.2.2 2004/07/19 19:30:50 drh Exp $
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 */
exprSplit(int nSlot,ExprInfo * aSlot,Expr * pExpr)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 */
getMask(ExprMaskSet * pMaskSet,int iCursor)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 */
exprTableUsage(ExprMaskSet * pMaskSet,Expr * p)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 */
allowedOp(int op)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 */
exprAnalyze(ExprMaskSet * pMaskSet,ExprInfo * pInfo)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 */
findSortingIndex(Table * pTab,int base,ExprList * pOrderBy,Index * pPreferredIdx,int nEqCol,int * pbRev)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 */
disableTerm(WhereLevel * pLevel,Expr ** ppExpr)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 */
sqliteWhereBegin(Parse * pParse,SrcList * pTabList,Expr * pWhere,int pushKey,ExprList ** ppOrderBy)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 */
sqliteWhereEnd(WhereInfo * pWInfo)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 }
1236