xref: /sqlite-3.40.0/src/update.c (revision fd3b2226)
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 file contains C code routines that are called by the parser
13 ** to handle UPDATE statements.
14 **
15 ** $Id: update.c,v 1.207 2009/08/08 18:01:08 drh Exp $
16 */
17 #include "sqliteInt.h"
18 
19 #ifndef SQLITE_OMIT_VIRTUALTABLE
20 /* Forward declaration */
21 static void updateVirtualTable(
22   Parse *pParse,       /* The parsing context */
23   SrcList *pSrc,       /* The virtual table to be modified */
24   Table *pTab,         /* The virtual table */
25   ExprList *pChanges,  /* The columns to change in the UPDATE statement */
26   Expr *pRowidExpr,    /* Expression used to recompute the rowid */
27   int *aXRef,          /* Mapping from columns of pTab to entries in pChanges */
28   Expr *pWhere         /* WHERE clause of the UPDATE statement */
29 );
30 #endif /* SQLITE_OMIT_VIRTUALTABLE */
31 
32 /*
33 ** The most recently coded instruction was an OP_Column to retrieve the
34 ** i-th column of table pTab. This routine sets the P4 parameter of the
35 ** OP_Column to the default value, if any.
36 **
37 ** The default value of a column is specified by a DEFAULT clause in the
38 ** column definition. This was either supplied by the user when the table
39 ** was created, or added later to the table definition by an ALTER TABLE
40 ** command. If the latter, then the row-records in the table btree on disk
41 ** may not contain a value for the column and the default value, taken
42 ** from the P4 parameter of the OP_Column instruction, is returned instead.
43 ** If the former, then all row-records are guaranteed to include a value
44 ** for the column and the P4 value is not required.
45 **
46 ** Column definitions created by an ALTER TABLE command may only have
47 ** literal default values specified: a number, null or a string. (If a more
48 ** complicated default expression value was provided, it is evaluated
49 ** when the ALTER TABLE is executed and one of the literal values written
50 ** into the sqlite_master table.)
51 **
52 ** Therefore, the P4 parameter is only required if the default value for
53 ** the column is a literal number, string or null. The sqlite3ValueFromExpr()
54 ** function is capable of transforming these types of expressions into
55 ** sqlite3_value objects.
56 **
57 ** If parameter iReg is not negative, code an OP_RealAffinity instruction
58 ** on register iReg. This is used when an equivalent integer value is
59 ** stored in place of an 8-byte floating point value in order to save
60 ** space.
61 */
62 void sqlite3ColumnDefault(Vdbe *v, Table *pTab, int i, int iReg){
63   assert( pTab!=0 );
64   if( !pTab->pSelect ){
65     sqlite3_value *pValue;
66     u8 enc = ENC(sqlite3VdbeDb(v));
67     Column *pCol = &pTab->aCol[i];
68     VdbeComment((v, "%s.%s", pTab->zName, pCol->zName));
69     assert( i<pTab->nCol );
70     sqlite3ValueFromExpr(sqlite3VdbeDb(v), pCol->pDflt, enc,
71                          pCol->affinity, &pValue);
72     if( pValue ){
73       sqlite3VdbeChangeP4(v, -1, (const char *)pValue, P4_MEM);
74     }
75 #ifndef SQLITE_OMIT_FLOATING_POINT
76     if( iReg>=0 && pTab->aCol[i].affinity==SQLITE_AFF_REAL ){
77       sqlite3VdbeAddOp1(v, OP_RealAffinity, iReg);
78     }
79 #endif
80   }
81 }
82 
83 /*
84 ** Process an UPDATE statement.
85 **
86 **   UPDATE OR IGNORE table_wxyz SET a=b, c=d WHERE e<5 AND f NOT NULL;
87 **          \_______/ \________/     \______/       \________________/
88 *            onError   pTabList      pChanges             pWhere
89 */
90 void sqlite3Update(
91   Parse *pParse,         /* The parser context */
92   SrcList *pTabList,     /* The table in which we should change things */
93   ExprList *pChanges,    /* Things to be changed */
94   Expr *pWhere,          /* The WHERE clause.  May be null */
95   int onError            /* How to handle constraint errors */
96 ){
97   int i, j;              /* Loop counters */
98   Table *pTab;           /* The table to be updated */
99   int addr = 0;          /* VDBE instruction address of the start of the loop */
100   WhereInfo *pWInfo;     /* Information about the WHERE clause */
101   Vdbe *v;               /* The virtual database engine */
102   Index *pIdx;           /* For looping over indices */
103   int nIdx;              /* Number of indices that need updating */
104   int iCur;              /* VDBE Cursor number of pTab */
105   sqlite3 *db;           /* The database structure */
106   int *aRegIdx = 0;      /* One register assigned to each index to be updated */
107   int *aXRef = 0;        /* aXRef[i] is the index in pChanges->a[] of the
108                          ** an expression for the i-th column of the table.
109                          ** aXRef[i]==-1 if the i-th column is not changed. */
110   int chngRowid;         /* True if the record number is being changed */
111   Expr *pRowidExpr = 0;  /* Expression defining the new record number */
112   int openAll = 0;       /* True if all indices need to be opened */
113   AuthContext sContext;  /* The authorization context */
114   NameContext sNC;       /* The name-context to resolve expressions in */
115   int iDb;               /* Database containing the table being updated */
116   int j1;                /* Addresses of jump instructions */
117   int okOnePass;         /* True for one-pass algorithm without the FIFO */
118   int hasFK;             /* True if foreign key processing is required */
119 
120 #ifndef SQLITE_OMIT_TRIGGER
121   int isView;                  /* Trying to update a view */
122   Trigger *pTrigger;           /* List of triggers on pTab, if required */
123 #endif
124 
125   /* Register Allocations */
126   int regRowCount = 0;   /* A count of rows changed */
127   int regOldRowid;       /* The old rowid */
128   int regNewRowid;       /* The new rowid */
129   int regNew;
130   int regOld = 0;
131   int regRowSet = 0;     /* Rowset of rows to be updated */
132   int regRec;            /* Register used for new table record to insert */
133 
134   memset(&sContext, 0, sizeof(sContext));
135   db = pParse->db;
136   if( pParse->nErr || db->mallocFailed ){
137     goto update_cleanup;
138   }
139   assert( pTabList->nSrc==1 );
140 
141   /* Locate the table which we want to update.
142   */
143   pTab = sqlite3SrcListLookup(pParse, pTabList);
144   if( pTab==0 ) goto update_cleanup;
145   iDb = sqlite3SchemaToIndex(pParse->db, pTab->pSchema);
146 
147   /* Figure out if we have any triggers and if the table being
148   ** updated is a view.
149   */
150 #ifndef SQLITE_OMIT_TRIGGER
151   pTrigger = sqlite3TriggersExist(pParse, pTab, TK_UPDATE, pChanges, 0);
152   isView = pTab->pSelect!=0;
153 #else
154 # define pTrigger 0
155 # define isView 0
156 #endif
157 #ifdef SQLITE_OMIT_VIEW
158 # undef isView
159 # define isView 0
160 #endif
161 
162   if( sqlite3ViewGetColumnNames(pParse, pTab) ){
163     goto update_cleanup;
164   }
165   if( sqlite3IsReadOnly(pParse, pTab, (pTrigger?1:0)) ){
166     goto update_cleanup;
167   }
168   aXRef = sqlite3DbMallocRaw(db, sizeof(int) * pTab->nCol );
169   if( aXRef==0 ) goto update_cleanup;
170   for(i=0; i<pTab->nCol; i++) aXRef[i] = -1;
171 
172   /* Allocate a cursors for the main database table and for all indices.
173   ** The index cursors might not be used, but if they are used they
174   ** need to occur right after the database cursor.  So go ahead and
175   ** allocate enough space, just in case.
176   */
177   pTabList->a[0].iCursor = iCur = pParse->nTab++;
178   for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
179     pParse->nTab++;
180   }
181 
182   /* Initialize the name-context */
183   memset(&sNC, 0, sizeof(sNC));
184   sNC.pParse = pParse;
185   sNC.pSrcList = pTabList;
186 
187   /* Resolve the column names in all the expressions of the
188   ** of the UPDATE statement.  Also find the column index
189   ** for each column to be updated in the pChanges array.  For each
190   ** column to be updated, make sure we have authorization to change
191   ** that column.
192   */
193   chngRowid = 0;
194   for(i=0; i<pChanges->nExpr; i++){
195     if( sqlite3ResolveExprNames(&sNC, pChanges->a[i].pExpr) ){
196       goto update_cleanup;
197     }
198     for(j=0; j<pTab->nCol; j++){
199       if( sqlite3StrICmp(pTab->aCol[j].zName, pChanges->a[i].zName)==0 ){
200         if( j==pTab->iPKey ){
201           chngRowid = 1;
202           pRowidExpr = pChanges->a[i].pExpr;
203         }
204         aXRef[j] = i;
205         break;
206       }
207     }
208     if( j>=pTab->nCol ){
209       if( sqlite3IsRowid(pChanges->a[i].zName) ){
210         chngRowid = 1;
211         pRowidExpr = pChanges->a[i].pExpr;
212       }else{
213         sqlite3ErrorMsg(pParse, "no such column: %s", pChanges->a[i].zName);
214         goto update_cleanup;
215       }
216     }
217 #ifndef SQLITE_OMIT_AUTHORIZATION
218     {
219       int rc;
220       rc = sqlite3AuthCheck(pParse, SQLITE_UPDATE, pTab->zName,
221                            pTab->aCol[j].zName, db->aDb[iDb].zName);
222       if( rc==SQLITE_DENY ){
223         goto update_cleanup;
224       }else if( rc==SQLITE_IGNORE ){
225         aXRef[j] = -1;
226       }
227     }
228 #endif
229   }
230 
231   hasFK = sqlite3FkRequired(pParse, pTab, aXRef, chngRowid);
232 
233   /* Allocate memory for the array aRegIdx[].  There is one entry in the
234   ** array for each index associated with table being updated.  Fill in
235   ** the value with a register number for indices that are to be used
236   ** and with zero for unused indices.
237   */
238   for(nIdx=0, pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext, nIdx++){}
239   if( nIdx>0 ){
240     aRegIdx = sqlite3DbMallocRaw(db, sizeof(Index*) * nIdx );
241     if( aRegIdx==0 ) goto update_cleanup;
242   }
243   for(j=0, pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext, j++){
244     int reg;
245     if( chngRowid ){
246       reg = ++pParse->nMem;
247     }else{
248       reg = 0;
249       for(i=0; i<pIdx->nColumn; i++){
250         if( aXRef[pIdx->aiColumn[i]]>=0 ){
251           reg = ++pParse->nMem;
252           break;
253         }
254       }
255     }
256     aRegIdx[j] = reg;
257   }
258 
259   /* Begin generating code. */
260   v = sqlite3GetVdbe(pParse);
261   if( v==0 ) goto update_cleanup;
262   if( pParse->nested==0 ) sqlite3VdbeCountChanges(v);
263   sqlite3BeginWriteOperation(pParse, 1, iDb);
264 
265 #ifndef SQLITE_OMIT_VIRTUALTABLE
266   /* Virtual tables must be handled separately */
267   if( IsVirtual(pTab) ){
268     updateVirtualTable(pParse, pTabList, pTab, pChanges, pRowidExpr, aXRef,
269                        pWhere);
270     pWhere = 0;
271     pTabList = 0;
272     goto update_cleanup;
273   }
274 #endif
275 
276   /* Allocate required registers. */
277   regOldRowid = regNewRowid = ++pParse->nMem;
278   if( pTrigger || hasFK ){
279     regOld = pParse->nMem + 1;
280     pParse->nMem += pTab->nCol;
281   }
282   if( chngRowid || pTrigger || hasFK ){
283     regNewRowid = ++pParse->nMem;
284   }
285   regNew = pParse->nMem + 1;
286   pParse->nMem += pTab->nCol;
287   regRec = ++pParse->nMem;
288 
289   /* Start the view context. */
290   if( isView ){
291     sqlite3AuthContextPush(pParse, &sContext, pTab->zName);
292   }
293 
294   /* If we are trying to update a view, realize that view into
295   ** a ephemeral table.
296   */
297 #if !defined(SQLITE_OMIT_VIEW) && !defined(SQLITE_OMIT_TRIGGER)
298   if( isView ){
299     sqlite3MaterializeView(pParse, pTab, pWhere, iCur);
300   }
301 #endif
302 
303   /* Resolve the column names in all the expressions in the
304   ** WHERE clause.
305   */
306   if( sqlite3ResolveExprNames(&sNC, pWhere) ){
307     goto update_cleanup;
308   }
309 
310   /* Begin the database scan
311   */
312   sqlite3VdbeAddOp2(v, OP_Null, 0, regOldRowid);
313   pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere,0, WHERE_ONEPASS_DESIRED);
314   if( pWInfo==0 ) goto update_cleanup;
315   okOnePass = pWInfo->okOnePass;
316 
317   /* Remember the rowid of every item to be updated.
318   */
319   sqlite3VdbeAddOp2(v, OP_Rowid, iCur, regOldRowid);
320   if( !okOnePass ){
321     regRowSet = ++pParse->nMem;
322     sqlite3VdbeAddOp2(v, OP_RowSetAdd, regRowSet, regOldRowid);
323   }
324 
325   /* End the database scan loop.
326   */
327   sqlite3WhereEnd(pWInfo);
328 
329   /* Initialize the count of updated rows
330   */
331   if( (db->flags & SQLITE_CountRows) && !pParse->pTriggerTab ){
332     regRowCount = ++pParse->nMem;
333     sqlite3VdbeAddOp2(v, OP_Integer, 0, regRowCount);
334   }
335 
336   if( !isView ){
337     /*
338     ** Open every index that needs updating.  Note that if any
339     ** index could potentially invoke a REPLACE conflict resolution
340     ** action, then we need to open all indices because we might need
341     ** to be deleting some records.
342     */
343     if( !okOnePass ) sqlite3OpenTable(pParse, iCur, iDb, pTab, OP_OpenWrite);
344     if( onError==OE_Replace ){
345       openAll = 1;
346     }else{
347       openAll = 0;
348       for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
349         if( pIdx->onError==OE_Replace ){
350           openAll = 1;
351           break;
352         }
353       }
354     }
355     for(i=0, pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext, i++){
356       if( openAll || aRegIdx[i]>0 ){
357         KeyInfo *pKey = sqlite3IndexKeyinfo(pParse, pIdx);
358         sqlite3VdbeAddOp4(v, OP_OpenWrite, iCur+i+1, pIdx->tnum, iDb,
359                        (char*)pKey, P4_KEYINFO_HANDOFF);
360         assert( pParse->nTab>iCur+i+1 );
361       }
362     }
363   }
364 
365   /* Top of the update loop */
366   if( okOnePass ){
367     int a1 = sqlite3VdbeAddOp1(v, OP_NotNull, regOldRowid);
368     addr = sqlite3VdbeAddOp0(v, OP_Goto);
369     sqlite3VdbeJumpHere(v, a1);
370   }else{
371     addr = sqlite3VdbeAddOp3(v, OP_RowSetRead, regRowSet, 0, regOldRowid);
372   }
373 
374   /* Make cursor iCur point to the record that is being updated. If
375   ** this record does not exist for some reason (deleted by a trigger,
376   ** for example, then jump to the next iteration of the RowSet loop.  */
377   sqlite3VdbeAddOp3(v, OP_NotExists, iCur, addr, regOldRowid);
378 
379   /* If the record number will change, set register regNewRowid to
380   ** contain the new value. If the record number is not being modified,
381   ** then regNewRowid is the same register as regOldRowid, which is
382   ** already populated.  */
383   assert( chngRowid || pTrigger || hasFK || regOldRowid==regNewRowid );
384   if( chngRowid ){
385     sqlite3ExprCode(pParse, pRowidExpr, regNewRowid);
386     sqlite3VdbeAddOp1(v, OP_MustBeInt, regNewRowid);
387   }
388 
389   /* If there are triggers on this table, populate an array of registers
390   ** with the required old.* column data.  */
391   if( hasFK || pTrigger ){
392     u32 oldmask = (hasFK ? sqlite3FkOldmask(pParse, pTab) : 0);
393     oldmask |= sqlite3TriggerOldmask(pParse, pTrigger, pChanges, pTab, onError);
394     for(i=0; i<pTab->nCol; i++){
395       if( aXRef[i]<0 || oldmask==0xffffffff || (oldmask & (1<<i)) ){
396         sqlite3VdbeAddOp3(v, OP_Column, iCur, i, regOld+i);
397         sqlite3ColumnDefault(v, pTab, i, regOld+i);
398       }else{
399         sqlite3VdbeAddOp2(v, OP_Null, 0, regOld+i);
400       }
401     }
402     if( chngRowid==0 ){
403       sqlite3VdbeAddOp2(v, OP_Copy, regOldRowid, regNewRowid);
404     }
405   }
406 
407   /* Populate the array of registers beginning at regNew with the new
408   ** row data. This array is used to check constaints, create the new
409   ** table and index records, and as the values for any new.* references
410   ** made by triggers.  */
411   for(i=0; i<pTab->nCol; i++){
412     if( i==pTab->iPKey ){
413       sqlite3VdbeAddOp2(v, OP_Null, 0, regNew+i);
414     }else{
415       j = aXRef[i];
416       if( j<0 ){
417         sqlite3VdbeAddOp3(v, OP_Column, iCur, i, regNew+i);
418         sqlite3ColumnDefault(v, pTab, i, regNew+i);
419       }else{
420         sqlite3ExprCode(pParse, pChanges->a[j].pExpr, regNew+i);
421       }
422     }
423   }
424 
425   /* Fire any BEFORE UPDATE triggers. This happens before constraints are
426   ** verified. One could argue that this is wrong.  */
427   if( pTrigger ){
428     sqlite3VdbeAddOp2(v, OP_Affinity, regNew, pTab->nCol);
429     sqlite3TableAffinityStr(v, pTab);
430     sqlite3CodeRowTrigger(pParse, pTrigger, TK_UPDATE, pChanges,
431         TRIGGER_BEFORE, pTab, regOldRowid, onError, addr);
432 
433     /* The row-trigger may have deleted the row being updated. In this
434     ** case, jump to the next row. No updates or AFTER triggers are
435     ** required. This behaviour - what happens when the row being updated
436     ** is deleted or renamed by a BEFORE trigger - is left undefined in the
437     ** documentation.  */
438     sqlite3VdbeAddOp3(v, OP_NotExists, iCur, addr, regOldRowid);
439   }
440 
441   if( !isView ){
442 
443     /* Do constraint checks. */
444     sqlite3GenerateConstraintChecks(pParse, pTab, iCur, regNewRowid,
445         aRegIdx, (chngRowid?regOldRowid:0), 1, onError, addr, 0);
446 
447     /* Do FK constraint checks. */
448     if( hasFK ){
449       sqlite3FkCheck(pParse, pTab, regOldRowid, 0);
450     }
451 
452     /* Delete the index entries associated with the current record.  */
453     j1 = sqlite3VdbeAddOp3(v, OP_NotExists, iCur, 0, regOldRowid);
454     sqlite3GenerateRowIndexDelete(pParse, pTab, iCur, aRegIdx);
455 
456     /* If changing the record number, delete the old record.  */
457     if( hasFK || chngRowid ){
458       sqlite3VdbeAddOp2(v, OP_Delete, iCur, 0);
459     }
460     sqlite3VdbeJumpHere(v, j1);
461 
462     if( hasFK ){
463       sqlite3FkCheck(pParse, pTab, 0, regNewRowid);
464     }
465 
466     /* Insert the new index entries and the new record. */
467     sqlite3CompleteInsertion(pParse, pTab, iCur, regNewRowid, aRegIdx, 1, 0, 0);
468 
469     /* Do any ON CASCADE, SET NULL or SET DEFAULT operations required to
470     ** handle rows (possibly in other tables) that refer via a foreign key
471     ** to the row just updated. */
472     if( hasFK ){
473       sqlite3FkActions(pParse, pTab, pChanges, regOldRowid);
474     }
475   }
476 
477   /* Increment the row counter
478   */
479   if( (db->flags & SQLITE_CountRows) && !pParse->pTriggerTab){
480     sqlite3VdbeAddOp2(v, OP_AddImm, regRowCount, 1);
481   }
482 
483   sqlite3CodeRowTrigger(pParse, pTrigger, TK_UPDATE, pChanges,
484       TRIGGER_AFTER, pTab, regOldRowid, onError, addr);
485 
486   /* Repeat the above with the next record to be updated, until
487   ** all record selected by the WHERE clause have been updated.
488   */
489   sqlite3VdbeAddOp2(v, OP_Goto, 0, addr);
490   sqlite3VdbeJumpHere(v, addr);
491 
492   /* Close all tables */
493   for(i=0, pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext, i++){
494     if( openAll || aRegIdx[i]>0 ){
495       sqlite3VdbeAddOp2(v, OP_Close, iCur+i+1, 0);
496     }
497   }
498   sqlite3VdbeAddOp2(v, OP_Close, iCur, 0);
499 
500   /* Update the sqlite_sequence table by storing the content of the
501   ** maximum rowid counter values recorded while inserting into
502   ** autoincrement tables.
503   */
504   if( pParse->nested==0 && pParse->pTriggerTab==0 ){
505     sqlite3AutoincrementEnd(pParse);
506   }
507 
508   /*
509   ** Return the number of rows that were changed. If this routine is
510   ** generating code because of a call to sqlite3NestedParse(), do not
511   ** invoke the callback function.
512   */
513   if( (db->flags&SQLITE_CountRows) && !pParse->pTriggerTab && !pParse->nested ){
514     sqlite3VdbeAddOp2(v, OP_ResultRow, regRowCount, 1);
515     sqlite3VdbeSetNumCols(v, 1);
516     sqlite3VdbeSetColName(v, 0, COLNAME_NAME, "rows updated", SQLITE_STATIC);
517   }
518 
519 update_cleanup:
520   sqlite3AuthContextPop(&sContext);
521   sqlite3DbFree(db, aRegIdx);
522   sqlite3DbFree(db, aXRef);
523   sqlite3SrcListDelete(db, pTabList);
524   sqlite3ExprListDelete(db, pChanges);
525   sqlite3ExprDelete(db, pWhere);
526   return;
527 }
528 /* Make sure "isView" and other macros defined above are undefined. Otherwise
529 ** thely may interfere with compilation of other functions in this file
530 ** (or in another file, if this file becomes part of the amalgamation).  */
531 #ifdef isView
532  #undef isView
533 #endif
534 #ifdef pTrigger
535  #undef pTrigger
536 #endif
537 
538 #ifndef SQLITE_OMIT_VIRTUALTABLE
539 /*
540 ** Generate code for an UPDATE of a virtual table.
541 **
542 ** The strategy is that we create an ephemerial table that contains
543 ** for each row to be changed:
544 **
545 **   (A)  The original rowid of that row.
546 **   (B)  The revised rowid for the row. (note1)
547 **   (C)  The content of every column in the row.
548 **
549 ** Then we loop over this ephemeral table and for each row in
550 ** the ephermeral table call VUpdate.
551 **
552 ** When finished, drop the ephemeral table.
553 **
554 ** (note1) Actually, if we know in advance that (A) is always the same
555 ** as (B) we only store (A), then duplicate (A) when pulling
556 ** it out of the ephemeral table before calling VUpdate.
557 */
558 static void updateVirtualTable(
559   Parse *pParse,       /* The parsing context */
560   SrcList *pSrc,       /* The virtual table to be modified */
561   Table *pTab,         /* The virtual table */
562   ExprList *pChanges,  /* The columns to change in the UPDATE statement */
563   Expr *pRowid,        /* Expression used to recompute the rowid */
564   int *aXRef,          /* Mapping from columns of pTab to entries in pChanges */
565   Expr *pWhere         /* WHERE clause of the UPDATE statement */
566 ){
567   Vdbe *v = pParse->pVdbe;  /* Virtual machine under construction */
568   ExprList *pEList = 0;     /* The result set of the SELECT statement */
569   Select *pSelect = 0;      /* The SELECT statement */
570   Expr *pExpr;              /* Temporary expression */
571   int ephemTab;             /* Table holding the result of the SELECT */
572   int i;                    /* Loop counter */
573   int addr;                 /* Address of top of loop */
574   int iReg;                 /* First register in set passed to OP_VUpdate */
575   sqlite3 *db = pParse->db; /* Database connection */
576   const char *pVTab = (const char*)sqlite3GetVTable(db, pTab);
577   SelectDest dest;
578 
579   /* Construct the SELECT statement that will find the new values for
580   ** all updated rows.
581   */
582   pEList = sqlite3ExprListAppend(pParse, 0,
583                                  sqlite3CreateIdExpr(pParse, "_rowid_"));
584   if( pRowid ){
585     pEList = sqlite3ExprListAppend(pParse, pEList,
586                                    sqlite3ExprDup(db, pRowid, 0));
587   }
588   assert( pTab->iPKey<0 );
589   for(i=0; i<pTab->nCol; i++){
590     if( aXRef[i]>=0 ){
591       pExpr = sqlite3ExprDup(db, pChanges->a[aXRef[i]].pExpr, 0);
592     }else{
593       pExpr = sqlite3CreateIdExpr(pParse, pTab->aCol[i].zName);
594     }
595     pEList = sqlite3ExprListAppend(pParse, pEList, pExpr);
596   }
597   pSelect = sqlite3SelectNew(pParse, pEList, pSrc, pWhere, 0, 0, 0, 0, 0, 0);
598 
599   /* Create the ephemeral table into which the update results will
600   ** be stored.
601   */
602   assert( v );
603   ephemTab = pParse->nTab++;
604   sqlite3VdbeAddOp2(v, OP_OpenEphemeral, ephemTab, pTab->nCol+1+(pRowid!=0));
605 
606   /* fill the ephemeral table
607   */
608   sqlite3SelectDestInit(&dest, SRT_Table, ephemTab);
609   sqlite3Select(pParse, pSelect, &dest);
610 
611   /* Generate code to scan the ephemeral table and call VUpdate. */
612   iReg = ++pParse->nMem;
613   pParse->nMem += pTab->nCol+1;
614   addr = sqlite3VdbeAddOp2(v, OP_Rewind, ephemTab, 0);
615   sqlite3VdbeAddOp3(v, OP_Column,  ephemTab, 0, iReg);
616   sqlite3VdbeAddOp3(v, OP_Column, ephemTab, (pRowid?1:0), iReg+1);
617   for(i=0; i<pTab->nCol; i++){
618     sqlite3VdbeAddOp3(v, OP_Column, ephemTab, i+1+(pRowid!=0), iReg+2+i);
619   }
620   sqlite3VtabMakeWritable(pParse, pTab);
621   sqlite3VdbeAddOp4(v, OP_VUpdate, 0, pTab->nCol+2, iReg, pVTab, P4_VTAB);
622   sqlite3MayAbort(pParse);
623   sqlite3VdbeAddOp2(v, OP_Next, ephemTab, addr+1);
624   sqlite3VdbeJumpHere(v, addr);
625   sqlite3VdbeAddOp2(v, OP_Close, ephemTab, 0);
626 
627   /* Cleanup */
628   sqlite3SelectDelete(db, pSelect);
629 }
630 #endif /* SQLITE_OMIT_VIRTUALTABLE */
631