extensions/sqlite/sqlite-source/update.c
author Asher Baker <asherkin@gmail.com>
Thu Apr 26 16:58:18 2012 +0100 (2012-04-26)
changeset 3488 bee90c8ef6c3
parent 1952 b7aa2b626807
permissions -rw-r--r--
Fixed client serials not being unique on Windows (bug 5285, r=psychonic).
     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 ** $Id$
    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 P3 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 P3 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 P3 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 P3 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 void sqlite3ColumnDefault(Vdbe *v, Table *pTab, int i){
    58   if( pTab && !pTab->pSelect ){
    59     sqlite3_value *pValue;
    60     u8 enc = ENC(sqlite3VdbeDb(v));
    61     Column *pCol = &pTab->aCol[i];
    62     assert( i<pTab->nCol );
    63     sqlite3ValueFromExpr(sqlite3VdbeDb(v), pCol->pDflt, enc, pCol->affinity, &pValue);
    64     if( pValue ){
    65       sqlite3VdbeChangeP3(v, -1, (const char *)pValue, P3_MEM);
    66     }else{
    67       VdbeComment((v, "# %s.%s", pTab->zName, pCol->zName));
    68     }
    69   }
    70 }
    71 
    72 /*
    73 ** Process an UPDATE statement.
    74 **
    75 **   UPDATE OR IGNORE table_wxyz SET a=b, c=d WHERE e<5 AND f NOT NULL;
    76 **          \_______/ \________/     \______/       \________________/
    77 *            onError   pTabList      pChanges             pWhere
    78 */
    79 void sqlite3Update(
    80   Parse *pParse,         /* The parser context */
    81   SrcList *pTabList,     /* The table in which we should change things */
    82   ExprList *pChanges,    /* Things to be changed */
    83   Expr *pWhere,          /* The WHERE clause.  May be null */
    84   int onError            /* How to handle constraint errors */
    85 ){
    86   int i, j;              /* Loop counters */
    87   Table *pTab;           /* The table to be updated */
    88   int addr = 0;          /* VDBE instruction address of the start of the loop */
    89   WhereInfo *pWInfo;     /* Information about the WHERE clause */
    90   Vdbe *v;               /* The virtual database engine */
    91   Index *pIdx;           /* For looping over indices */
    92   int nIdx;              /* Number of indices that need updating */
    93   int nIdxTotal;         /* Total number of indices */
    94   int iCur;              /* VDBE Cursor number of pTab */
    95   sqlite3 *db;           /* The database structure */
    96   Index **apIdx = 0;     /* An array of indices that need updating too */
    97   char *aIdxUsed = 0;    /* aIdxUsed[i]==1 if the i-th index is used */
    98   int *aXRef = 0;        /* aXRef[i] is the index in pChanges->a[] of the
    99                          ** an expression for the i-th column of the table.
   100                          ** aXRef[i]==-1 if the i-th column is not changed. */
   101   int chngRowid;         /* True if the record number is being changed */
   102   Expr *pRowidExpr = 0;  /* Expression defining the new record number */
   103   int openAll = 0;       /* True if all indices need to be opened */
   104   AuthContext sContext;  /* The authorization context */
   105   NameContext sNC;       /* The name-context to resolve expressions in */
   106   int iDb;               /* Database containing the table being updated */
   107   int memCnt = 0;        /* Memory cell used for counting rows changed */
   108 
   109 #ifndef SQLITE_OMIT_TRIGGER
   110   int isView;                  /* Trying to update a view */
   111   int triggers_exist = 0;      /* True if any row triggers exist */
   112 #endif
   113 
   114   int newIdx      = -1;  /* index of trigger "new" temp table       */
   115   int oldIdx      = -1;  /* index of trigger "old" temp table       */
   116 
   117   sContext.pParse = 0;
   118   db = pParse->db;
   119   if( pParse->nErr || db->mallocFailed ){
   120     goto update_cleanup;
   121   }
   122   assert( pTabList->nSrc==1 );
   123 
   124   /* Locate the table which we want to update. 
   125   */
   126   pTab = sqlite3SrcListLookup(pParse, pTabList);
   127   if( pTab==0 ) goto update_cleanup;
   128   iDb = sqlite3SchemaToIndex(pParse->db, pTab->pSchema);
   129 
   130   /* Figure out if we have any triggers and if the table being
   131   ** updated is a view
   132   */
   133 #ifndef SQLITE_OMIT_TRIGGER
   134   triggers_exist = sqlite3TriggersExist(pParse, pTab, TK_UPDATE, pChanges);
   135   isView = pTab->pSelect!=0;
   136 #else
   137 # define triggers_exist 0
   138 # define isView 0
   139 #endif
   140 #ifdef SQLITE_OMIT_VIEW
   141 # undef isView
   142 # define isView 0
   143 #endif
   144 
   145   if( sqlite3IsReadOnly(pParse, pTab, triggers_exist) ){
   146     goto update_cleanup;
   147   }
   148   if( sqlite3ViewGetColumnNames(pParse, pTab) ){
   149     goto update_cleanup;
   150   }
   151   aXRef = sqlite3DbMallocRaw(db, sizeof(int) * pTab->nCol );
   152   if( aXRef==0 ) goto update_cleanup;
   153   for(i=0; i<pTab->nCol; i++) aXRef[i] = -1;
   154 
   155   /* If there are FOR EACH ROW triggers, allocate cursors for the
   156   ** special OLD and NEW tables
   157   */
   158   if( triggers_exist ){
   159     newIdx = pParse->nTab++;
   160     oldIdx = pParse->nTab++;
   161   }
   162 
   163   /* Allocate a cursors for the main database table and for all indices.
   164   ** The index cursors might not be used, but if they are used they
   165   ** need to occur right after the database cursor.  So go ahead and
   166   ** allocate enough space, just in case.
   167   */
   168   pTabList->a[0].iCursor = iCur = pParse->nTab++;
   169   for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
   170     pParse->nTab++;
   171   }
   172 
   173   /* Initialize the name-context */
   174   memset(&sNC, 0, sizeof(sNC));
   175   sNC.pParse = pParse;
   176   sNC.pSrcList = pTabList;
   177 
   178   /* Resolve the column names in all the expressions of the
   179   ** of the UPDATE statement.  Also find the column index
   180   ** for each column to be updated in the pChanges array.  For each
   181   ** column to be updated, make sure we have authorization to change
   182   ** that column.
   183   */
   184   chngRowid = 0;
   185   for(i=0; i<pChanges->nExpr; i++){
   186     if( sqlite3ExprResolveNames(&sNC, pChanges->a[i].pExpr) ){
   187       goto update_cleanup;
   188     }
   189     for(j=0; j<pTab->nCol; j++){
   190       if( sqlite3StrICmp(pTab->aCol[j].zName, pChanges->a[i].zName)==0 ){
   191         if( j==pTab->iPKey ){
   192           chngRowid = 1;
   193           pRowidExpr = pChanges->a[i].pExpr;
   194         }
   195         aXRef[j] = i;
   196         break;
   197       }
   198     }
   199     if( j>=pTab->nCol ){
   200       if( sqlite3IsRowid(pChanges->a[i].zName) ){
   201         chngRowid = 1;
   202         pRowidExpr = pChanges->a[i].pExpr;
   203       }else{
   204         sqlite3ErrorMsg(pParse, "no such column: %s", pChanges->a[i].zName);
   205         goto update_cleanup;
   206       }
   207     }
   208 #ifndef SQLITE_OMIT_AUTHORIZATION
   209     {
   210       int rc;
   211       rc = sqlite3AuthCheck(pParse, SQLITE_UPDATE, pTab->zName,
   212                            pTab->aCol[j].zName, db->aDb[iDb].zName);
   213       if( rc==SQLITE_DENY ){
   214         goto update_cleanup;
   215       }else if( rc==SQLITE_IGNORE ){
   216         aXRef[j] = -1;
   217       }
   218     }
   219 #endif
   220   }
   221 
   222   /* Allocate memory for the array apIdx[] and fill it with pointers to every
   223   ** index that needs to be updated.  Indices only need updating if their
   224   ** key includes one of the columns named in pChanges or if the record
   225   ** number of the original table entry is changing.
   226   */
   227   for(nIdx=nIdxTotal=0, pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext, nIdxTotal++){
   228     if( chngRowid ){
   229       i = 0;
   230     }else {
   231       for(i=0; i<pIdx->nColumn; i++){
   232         if( aXRef[pIdx->aiColumn[i]]>=0 ) break;
   233       }
   234     }
   235     if( i<pIdx->nColumn ) nIdx++;
   236   }
   237   if( nIdxTotal>0 ){
   238     apIdx = sqlite3DbMallocRaw(db, sizeof(Index*) * nIdx + nIdxTotal );
   239     if( apIdx==0 ) goto update_cleanup;
   240     aIdxUsed = (char*)&apIdx[nIdx];
   241   }
   242   for(nIdx=j=0, pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext, j++){
   243     if( chngRowid ){
   244       i = 0;
   245     }else{
   246       for(i=0; i<pIdx->nColumn; i++){
   247         if( aXRef[pIdx->aiColumn[i]]>=0 ) break;
   248       }
   249     }
   250     if( i<pIdx->nColumn ){
   251       apIdx[nIdx++] = pIdx;
   252       aIdxUsed[j] = 1;
   253     }else{
   254       aIdxUsed[j] = 0;
   255     }
   256   }
   257 
   258   /* Begin generating code.
   259   */
   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   /* Resolve the column names in all the expressions in the
   277   ** WHERE clause.
   278   */
   279   if( sqlite3ExprResolveNames(&sNC, pWhere) ){
   280     goto update_cleanup;
   281   }
   282 
   283   /* Start the view context
   284   */
   285   if( isView ){
   286     sqlite3AuthContextPush(pParse, &sContext, pTab->zName);
   287   }
   288 
   289   /* If we are trying to update a view, realize that view into
   290   ** a ephemeral table.
   291   */
   292   if( isView ){
   293     Select *pView;
   294     pView = sqlite3SelectDup(db, pTab->pSelect);
   295     sqlite3Select(pParse, pView, SRT_EphemTab, iCur, 0, 0, 0, 0);
   296     sqlite3SelectDelete(pView);
   297   }
   298 
   299   /* Begin the database scan
   300   */
   301   pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, 0);
   302   if( pWInfo==0 ) goto update_cleanup;
   303 
   304   /* Remember the rowid of every item to be updated.
   305   */
   306   sqlite3VdbeAddOp(v, IsVirtual(pTab) ? OP_VRowid : OP_Rowid, iCur, 0);
   307   sqlite3VdbeAddOp(v, OP_FifoWrite, 0, 0);
   308 
   309   /* End the database scan loop.
   310   */
   311   sqlite3WhereEnd(pWInfo);
   312 
   313   /* Initialize the count of updated rows
   314   */
   315   if( db->flags & SQLITE_CountRows && !pParse->trigStack ){
   316     memCnt = pParse->nMem++;
   317     sqlite3VdbeAddOp(v, OP_MemInt, 0, memCnt);
   318   }
   319 
   320   if( triggers_exist ){
   321     /* Create pseudo-tables for NEW and OLD
   322     */
   323     sqlite3VdbeAddOp(v, OP_OpenPseudo, oldIdx, 0);
   324     sqlite3VdbeAddOp(v, OP_SetNumColumns, oldIdx, pTab->nCol);
   325     sqlite3VdbeAddOp(v, OP_OpenPseudo, newIdx, 0);
   326     sqlite3VdbeAddOp(v, OP_SetNumColumns, newIdx, pTab->nCol);
   327 
   328     /* The top of the update loop for when there are triggers.
   329     */
   330     addr = sqlite3VdbeAddOp(v, OP_FifoRead, 0, 0);
   331 
   332     if( !isView ){
   333       sqlite3VdbeAddOp(v, OP_Dup, 0, 0);
   334       sqlite3VdbeAddOp(v, OP_Dup, 0, 0);
   335       /* Open a cursor and make it point to the record that is
   336       ** being updated.
   337       */
   338       sqlite3OpenTable(pParse, iCur, iDb, pTab, OP_OpenRead);
   339     }
   340     sqlite3VdbeAddOp(v, OP_MoveGe, iCur, 0);
   341 
   342     /* Generate the OLD table
   343     */
   344     sqlite3VdbeAddOp(v, OP_Rowid, iCur, 0);
   345     sqlite3VdbeAddOp(v, OP_RowData, iCur, 0);
   346     sqlite3VdbeAddOp(v, OP_Insert, oldIdx, 0);
   347 
   348     /* Generate the NEW table
   349     */
   350     if( chngRowid ){
   351       sqlite3ExprCodeAndCache(pParse, pRowidExpr);
   352     }else{
   353       sqlite3VdbeAddOp(v, OP_Rowid, iCur, 0);
   354     }
   355     for(i=0; i<pTab->nCol; i++){
   356       if( i==pTab->iPKey ){
   357         sqlite3VdbeAddOp(v, OP_Null, 0, 0);
   358         continue;
   359       }
   360       j = aXRef[i];
   361       if( j<0 ){
   362         sqlite3VdbeAddOp(v, OP_Column, iCur, i);
   363         sqlite3ColumnDefault(v, pTab, i);
   364       }else{
   365         sqlite3ExprCodeAndCache(pParse, pChanges->a[j].pExpr);
   366       }
   367     }
   368     sqlite3VdbeAddOp(v, OP_MakeRecord, pTab->nCol, 0);
   369     if( !isView ){
   370       sqlite3TableAffinityStr(v, pTab);
   371     }
   372     if( pParse->nErr ) goto update_cleanup;
   373     sqlite3VdbeAddOp(v, OP_Insert, newIdx, 0);
   374     if( !isView ){
   375       sqlite3VdbeAddOp(v, OP_Close, iCur, 0);
   376     }
   377 
   378     /* Fire the BEFORE and INSTEAD OF triggers
   379     */
   380     if( sqlite3CodeRowTrigger(pParse, TK_UPDATE, pChanges, TRIGGER_BEFORE, pTab,
   381           newIdx, oldIdx, onError, addr) ){
   382       goto update_cleanup;
   383     }
   384   }
   385 
   386   if( !isView && !IsVirtual(pTab) ){
   387     /* 
   388     ** Open every index that needs updating.  Note that if any
   389     ** index could potentially invoke a REPLACE conflict resolution 
   390     ** action, then we need to open all indices because we might need
   391     ** to be deleting some records.
   392     */
   393     sqlite3OpenTable(pParse, iCur, iDb, pTab, OP_OpenWrite); 
   394     if( onError==OE_Replace ){
   395       openAll = 1;
   396     }else{
   397       openAll = 0;
   398       for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
   399         if( pIdx->onError==OE_Replace ){
   400           openAll = 1;
   401           break;
   402         }
   403       }
   404     }
   405     for(i=0, pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext, i++){
   406       if( openAll || aIdxUsed[i] ){
   407         KeyInfo *pKey = sqlite3IndexKeyinfo(pParse, pIdx);
   408         sqlite3VdbeAddOp(v, OP_Integer, iDb, 0);
   409         sqlite3VdbeOp3(v, OP_OpenWrite, iCur+i+1, pIdx->tnum,
   410                        (char*)pKey, P3_KEYINFO_HANDOFF);
   411         assert( pParse->nTab>iCur+i+1 );
   412       }
   413     }
   414 
   415     /* Loop over every record that needs updating.  We have to load
   416     ** the old data for each record to be updated because some columns
   417     ** might not change and we will need to copy the old value.
   418     ** Also, the old data is needed to delete the old index entries.
   419     ** So make the cursor point at the old record.
   420     */
   421     if( !triggers_exist ){
   422       addr = sqlite3VdbeAddOp(v, OP_FifoRead, 0, 0);
   423       sqlite3VdbeAddOp(v, OP_Dup, 0, 0);
   424     }
   425     sqlite3VdbeAddOp(v, OP_NotExists, iCur, addr);
   426 
   427     /* If the record number will change, push the record number as it
   428     ** will be after the update. (The old record number is currently
   429     ** on top of the stack.)
   430     */
   431     if( chngRowid ){
   432       sqlite3ExprCode(pParse, pRowidExpr);
   433       sqlite3VdbeAddOp(v, OP_MustBeInt, 0, 0);
   434     }
   435 
   436     /* Compute new data for this record.  
   437     */
   438     for(i=0; i<pTab->nCol; i++){
   439       if( i==pTab->iPKey ){
   440         sqlite3VdbeAddOp(v, OP_Null, 0, 0);
   441         continue;
   442       }
   443       j = aXRef[i];
   444       if( j<0 ){
   445         sqlite3VdbeAddOp(v, OP_Column, iCur, i);
   446         sqlite3ColumnDefault(v, pTab, i);
   447       }else{
   448         sqlite3ExprCode(pParse, pChanges->a[j].pExpr);
   449       }
   450     }
   451 
   452     /* Do constraint checks
   453     */
   454     sqlite3GenerateConstraintChecks(pParse, pTab, iCur, aIdxUsed, chngRowid, 1,
   455                                    onError, addr);
   456 
   457     /* Delete the old indices for the current record.
   458     */
   459     sqlite3GenerateRowIndexDelete(v, pTab, iCur, aIdxUsed);
   460 
   461     /* If changing the record number, delete the old record.
   462     */
   463     if( chngRowid ){
   464       sqlite3VdbeAddOp(v, OP_Delete, iCur, 0);
   465     }
   466 
   467     /* Create the new index entries and the new record.
   468     */
   469     sqlite3CompleteInsertion(pParse, pTab, iCur, aIdxUsed, chngRowid, 1, -1, 0);
   470   }
   471 
   472   /* Increment the row counter 
   473   */
   474   if( db->flags & SQLITE_CountRows && !pParse->trigStack){
   475     sqlite3VdbeAddOp(v, OP_MemIncr, 1, memCnt);
   476   }
   477 
   478   /* If there are triggers, close all the cursors after each iteration
   479   ** through the loop.  The fire the after triggers.
   480   */
   481   if( triggers_exist ){
   482     if( !isView ){
   483       for(i=0, pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext, i++){
   484         if( openAll || aIdxUsed[i] )
   485           sqlite3VdbeAddOp(v, OP_Close, iCur+i+1, 0);
   486       }
   487       sqlite3VdbeAddOp(v, OP_Close, iCur, 0);
   488     }
   489     if( sqlite3CodeRowTrigger(pParse, TK_UPDATE, pChanges, TRIGGER_AFTER, pTab, 
   490           newIdx, oldIdx, onError, addr) ){
   491       goto update_cleanup;
   492     }
   493   }
   494 
   495   /* Repeat the above with the next record to be updated, until
   496   ** all record selected by the WHERE clause have been updated.
   497   */
   498   sqlite3VdbeAddOp(v, OP_Goto, 0, addr);
   499   sqlite3VdbeJumpHere(v, addr);
   500 
   501   /* Close all tables if there were no FOR EACH ROW triggers */
   502   if( !triggers_exist ){
   503     for(i=0, pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext, i++){
   504       if( openAll || aIdxUsed[i] ){
   505         sqlite3VdbeAddOp(v, OP_Close, iCur+i+1, 0);
   506       }
   507     }
   508     sqlite3VdbeAddOp(v, OP_Close, iCur, 0);
   509   }else{
   510     sqlite3VdbeAddOp(v, OP_Close, newIdx, 0);
   511     sqlite3VdbeAddOp(v, OP_Close, oldIdx, 0);
   512   }
   513 
   514   /*
   515   ** Return the number of rows that were changed. If this routine is 
   516   ** generating code because of a call to sqlite3NestedParse(), do not
   517   ** invoke the callback function.
   518   */
   519   if( db->flags & SQLITE_CountRows && !pParse->trigStack && pParse->nested==0 ){
   520     sqlite3VdbeAddOp(v, OP_MemLoad, memCnt, 0);
   521     sqlite3VdbeAddOp(v, OP_Callback, 1, 0);
   522     sqlite3VdbeSetNumCols(v, 1);
   523     sqlite3VdbeSetColName(v, 0, COLNAME_NAME, "rows updated", P3_STATIC);
   524   }
   525 
   526 update_cleanup:
   527   sqlite3AuthContextPop(&sContext);
   528   sqlite3_free(apIdx);
   529   sqlite3_free(aXRef);
   530   sqlite3SrcListDelete(pTabList);
   531   sqlite3ExprListDelete(pChanges);
   532   sqlite3ExprDelete(pWhere);
   533   return;
   534 }
   535 
   536 #ifndef SQLITE_OMIT_VIRTUALTABLE
   537 /*
   538 ** Generate code for an UPDATE of a virtual table.
   539 **
   540 ** The strategy is that we create an ephemerial table that contains
   541 ** for each row to be changed:
   542 **
   543 **   (A)  The original rowid of that row.
   544 **   (B)  The revised rowid for the row. (note1)
   545 **   (C)  The content of every column in the row.
   546 **
   547 ** Then we loop over this ephemeral table and for each row in
   548 ** the ephermeral table call VUpdate.
   549 **
   550 ** When finished, drop the ephemeral table.
   551 **
   552 ** (note1) Actually, if we know in advance that (A) is always the same
   553 ** as (B) we only store (A), then duplicate (A) when pulling
   554 ** it out of the ephemeral table before calling VUpdate.
   555 */
   556 static void updateVirtualTable(
   557   Parse *pParse,       /* The parsing context */
   558   SrcList *pSrc,       /* The virtual table to be modified */
   559   Table *pTab,         /* The virtual table */
   560   ExprList *pChanges,  /* The columns to change in the UPDATE statement */
   561   Expr *pRowid,        /* Expression used to recompute the rowid */
   562   int *aXRef,          /* Mapping from columns of pTab to entries in pChanges */
   563   Expr *pWhere         /* WHERE clause of the UPDATE statement */
   564 ){
   565   Vdbe *v = pParse->pVdbe;  /* Virtual machine under construction */
   566   ExprList *pEList = 0;     /* The result set of the SELECT statement */
   567   Select *pSelect = 0;      /* The SELECT statement */
   568   Expr *pExpr;              /* Temporary expression */
   569   int ephemTab;             /* Table holding the result of the SELECT */
   570   int i;                    /* Loop counter */
   571   int addr;                 /* Address of top of loop */
   572   sqlite3 *db = pParse->db; /* Database connection */
   573 
   574   /* Construct the SELECT statement that will find the new values for
   575   ** all updated rows. 
   576   */
   577   pEList = sqlite3ExprListAppend(pParse, 0, 
   578                                  sqlite3CreateIdExpr(pParse, "_rowid_"), 0);
   579   if( pRowid ){
   580     pEList = sqlite3ExprListAppend(pParse, pEList,
   581                                    sqlite3ExprDup(db, pRowid), 0);
   582   }
   583   assert( pTab->iPKey<0 );
   584   for(i=0; i<pTab->nCol; i++){
   585     if( aXRef[i]>=0 ){
   586       pExpr = sqlite3ExprDup(db, pChanges->a[aXRef[i]].pExpr);
   587     }else{
   588       pExpr = sqlite3CreateIdExpr(pParse, pTab->aCol[i].zName);
   589     }
   590     pEList = sqlite3ExprListAppend(pParse, pEList, pExpr, 0);
   591   }
   592   pSelect = sqlite3SelectNew(pParse, pEList, pSrc, pWhere, 0, 0, 0, 0, 0, 0);
   593   
   594   /* Create the ephemeral table into which the update results will
   595   ** be stored.
   596   */
   597   assert( v );
   598   ephemTab = pParse->nTab++;
   599   sqlite3VdbeAddOp(v, OP_OpenEphemeral, ephemTab, pTab->nCol+1+(pRowid!=0));
   600 
   601   /* fill the ephemeral table 
   602   */
   603   sqlite3Select(pParse, pSelect, SRT_Table, ephemTab, 0, 0, 0, 0);
   604 
   605   /*
   606   ** Generate code to scan the ephemeral table and call VDelete and
   607   ** VInsert
   608   */
   609   sqlite3VdbeAddOp(v, OP_Rewind, ephemTab, 0);
   610   addr = sqlite3VdbeCurrentAddr(v);
   611   sqlite3VdbeAddOp(v, OP_Column,  ephemTab, 0);
   612   if( pRowid ){
   613     sqlite3VdbeAddOp(v, OP_Column, ephemTab, 1);
   614   }else{
   615     sqlite3VdbeAddOp(v, OP_Dup, 0, 0);
   616   }
   617   for(i=0; i<pTab->nCol; i++){
   618     sqlite3VdbeAddOp(v, OP_Column, ephemTab, i+1+(pRowid!=0));
   619   }
   620   pParse->pVirtualLock = pTab;
   621   sqlite3VdbeOp3(v, OP_VUpdate, 0, pTab->nCol+2, 
   622                      (const char*)pTab->pVtab, P3_VTAB);
   623   sqlite3VdbeAddOp(v, OP_Next, ephemTab, addr);
   624   sqlite3VdbeJumpHere(v, addr-1);
   625   sqlite3VdbeAddOp(v, OP_Close, ephemTab, 0);
   626 
   627   /* Cleanup */
   628   sqlite3SelectDelete(pSelect);  
   629 }
   630 #endif /* SQLITE_OMIT_VIRTUALTABLE */