/*

 ** 2001 September 15

 **

 ** The author disclaims copyright to this source code.  In place of

 ** a legal notice, here is a blessing:

 **

 **    May you do good and not evil.

 **    May you find forgiveness for yourself and forgive others.

 **    May you share freely, never taking more than you give.

 **

 *************************************************************************

 ** This file contains C code routines that are called by the parser

 ** to handle UPDATE statements.

 **

 ** $Id: update.c,v 1.185 2008/10/09 18:48:31 danielk1977 Exp $

 */

 #include "sqliteInt.h"

 #ifndef SQLITE_OMIT_VIRTUALTABLE

 /* Forward declaration */

 static void updateVirtualTable(

   Parse *pParse,       /* The parsing context */

   SrcList *pSrc,       /* The virtual table to be modified */

   Table *pTab,         /* The virtual table */

   ExprList *pChanges,  /* The columns to change in the UPDATE statement */

   Expr *pRowidExpr,    /* Expression used to recompute the rowid */

   int *aXRef,          /* Mapping from columns of pTab to entries in pChanges */

   Expr *pWhere         /* WHERE clause of the UPDATE statement */

 );

 #endif /* SQLITE_OMIT_VIRTUALTABLE */

 /*

 ** The most recently coded instruction was an OP_Column to retrieve the

 ** i-th column of table pTab. This routine sets the P4 parameter of the 

 ** OP_Column to the default value, if any.

 **

 ** The default value of a column is specified by a DEFAULT clause in the 

 ** column definition. This was either supplied by the user when the table

 ** was created, or added later to the table definition by an ALTER TABLE

 ** command. If the latter, then the row-records in the table btree on disk

 ** may not contain a value for the column and the default value, taken

 ** from the P4 parameter of the OP_Column instruction, is returned instead.

 ** If the former, then all row-records are guaranteed to include a value

 ** for the column and the P4 value is not required.

 **

 ** Column definitions created by an ALTER TABLE command may only have 

 ** literal default values specified: a number, null or a string. (If a more

 ** complicated default expression value was provided, it is evaluated 

 ** when the ALTER TABLE is executed and one of the literal values written

 ** into the sqlite_master table.)

 **

 ** Therefore, the P4 parameter is only required if the default value for

 ** the column is a literal number, string or null. The sqlite3ValueFromExpr()

 ** function is capable of transforming these types of expressions into

 ** sqlite3_value objects.

 */

 void sqlite3ColumnDefault(Vdbe *v, Table *pTab, int i){

   if( pTab && !pTab->pSelect ){

     sqlite3_value *pValue;

     u8 enc = ENC(sqlite3VdbeDb(v));

     Column *pCol = &pTab->aCol[i];

     VdbeComment((v, "%s.%s", pTab->zName, pCol->zName));

     assert( i<pTab->nCol );

     sqlite3ValueFromExpr(sqlite3VdbeDb(v), pCol->pDflt, enc, 

                          pCol->affinity, &pValue);

     if( pValue ){

       sqlite3VdbeChangeP4(v, -1, (const char *)pValue, P4_MEM);

     }

   }

 }

 /*

 ** Process an UPDATE statement.

 **

 **   UPDATE OR IGNORE table_wxyz SET a=b, c=d WHERE e<5 AND f NOT NULL;

 **          \_______/ \________/     \______/       \________________/

 *            onError   pTabList      pChanges             pWhere

 */

 void sqlite3Update(

   Parse *pParse,         /* The parser context */

   SrcList *pTabList,     /* The table in which we should change things */

   ExprList *pChanges,    /* Things to be changed */

   Expr *pWhere,          /* The WHERE clause.  May be null */

   int onError            /* How to handle constraint errors */

 ){

   int i, j;              /* Loop counters */

   Table *pTab;           /* The table to be updated */

   int addr = 0;          /* VDBE instruction address of the start of the loop */

   WhereInfo *pWInfo;     /* Information about the WHERE clause */

   Vdbe *v;               /* The virtual database engine */

   Index *pIdx;           /* For looping over indices */

   int nIdx;              /* Number of indices that need updating */

   int iCur;              /* VDBE Cursor number of pTab */

   sqlite3 *db;           /* The database structure */

   int *aRegIdx = 0;      /* One register assigned to each index to be updated */

   int *aXRef = 0;        /* aXRef[i] is the index in pChanges->a[] of the

                          ** an expression for the i-th column of the table.

                          ** aXRef[i]==-1 if the i-th column is not changed. */

   int chngRowid;         /* True if the record number is being changed */

   Expr *pRowidExpr = 0;  /* Expression defining the new record number */

   int openAll = 0;       /* True if all indices need to be opened */

   AuthContext sContext;  /* The authorization context */

   NameContext sNC;       /* The name-context to resolve expressions in */

   int iDb;               /* Database containing the table being updated */

   int j1;                /* Addresses of jump instructions */

   int okOnePass;         /* True for one-pass algorithm without the FIFO */

 #ifndef SQLITE_OMIT_TRIGGER

   int isView;                  /* Trying to update a view */

   int triggers_exist = 0;      /* True if any row triggers exist */

 #endif

   int iBeginAfterTrigger;      /* Address of after trigger program */

   int iEndAfterTrigger;        /* Exit of after trigger program */

   int iBeginBeforeTrigger;     /* Address of before trigger program */

   int iEndBeforeTrigger;       /* Exit of before trigger program */

   u32 old_col_mask = 0;        /* Mask of OLD.* columns in use */

   u32 new_col_mask = 0;        /* Mask of NEW.* columns in use */

   int newIdx      = -1;  /* index of trigger "new" temp table       */

   int oldIdx      = -1;  /* index of trigger "old" temp table       */

   /* Register Allocations */

   int regRowCount = 0;   /* A count of rows changed */

   int regOldRowid;       /* The old rowid */

   int regNewRowid;       /* The new rowid */

   int regData;           /* New data for the row */

   sContext.pParse = 0;

   db = pParse->db;

   if( pParse->nErr || db->mallocFailed ){

     goto update_cleanup;

   }

   assert( pTabList->nSrc==1 );

   /* Locate the table which we want to update. 

   */

   pTab = sqlite3SrcListLookup(pParse, pTabList);

   if( pTab==0 ) goto update_cleanup;

   iDb = sqlite3SchemaToIndex(pParse->db, pTab->pSchema);

   /* Figure out if we have any triggers and if the table being

   ** updated is a view

   */

 #ifndef SQLITE_OMIT_TRIGGER

   triggers_exist = sqlite3TriggersExist(pParse, pTab, TK_UPDATE, pChanges);

   isView = pTab->pSelect!=0;

 #else

 # define triggers_exist 0

 # define isView 0

 #endif

 #ifdef SQLITE_OMIT_VIEW

 # undef isView

 # define isView 0

 #endif

   if( sqlite3IsReadOnly(pParse, pTab, triggers_exist) ){

     goto update_cleanup;

   }

   if( sqlite3ViewGetColumnNames(pParse, pTab) ){

     goto update_cleanup;

   }

   aXRef = sqlite3DbMallocRaw(db, sizeof(int) * pTab->nCol );

   if( aXRef==0 ) goto update_cleanup;

   for(i=0; i<pTab->nCol; i++) aXRef[i] = -1;

   /* If there are FOR EACH ROW triggers, allocate cursors for the

   ** special OLD and NEW tables

   */

   if( triggers_exist ){

     newIdx = pParse->nTab++;

     oldIdx = pParse->nTab++;

   }

   /* Allocate a cursors for the main database table and for all indices.

   ** The index cursors might not be used, but if they are used they

   ** need to occur right after the database cursor.  So go ahead and

   ** allocate enough space, just in case.

   */

   pTabList->a[0].iCursor = iCur = pParse->nTab++;

   for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){

     pParse->nTab++;

   }

   /* Initialize the name-context */

   memset(&sNC, 0, sizeof(sNC));

   sNC.pParse = pParse;

   sNC.pSrcList = pTabList;

   /* Resolve the column names in all the expressions of the

   ** of the UPDATE statement.  Also find the column index

   ** for each column to be updated in the pChanges array.  For each

   ** column to be updated, make sure we have authorization to change

   ** that column.

   */

   chngRowid = 0;

   for(i=0; i<pChanges->nExpr; i++){

     if( sqlite3ResolveExprNames(&sNC, pChanges->a[i].pExpr) ){

       goto update_cleanup;

     }

     for(j=0; j<pTab->nCol; j++){

       if( sqlite3StrICmp(pTab->aCol[j].zName, pChanges->a[i].zName)==0 ){

         if( j==pTab->iPKey ){

           chngRowid = 1;

           pRowidExpr = pChanges->a[i].pExpr;

         }

         aXRef[j] = i;

         break;

       }

     }

     if( j>=pTab->nCol ){

       if( sqlite3IsRowid(pChanges->a[i].zName) ){

         chngRowid = 1;

         pRowidExpr = pChanges->a[i].pExpr;

       }else{

         sqlite3ErrorMsg(pParse, "no such column: %s", pChanges->a[i].zName);

         goto update_cleanup;

       }

     }

 #ifndef SQLITE_OMIT_AUTHORIZATION

     {

       int rc;

       rc = sqlite3AuthCheck(pParse, SQLITE_UPDATE, pTab->zName,

                            pTab->aCol[j].zName, db->aDb[iDb].zName);

       if( rc==SQLITE_DENY ){

         goto update_cleanup;

       }else if( rc==SQLITE_IGNORE ){

         aXRef[j] = -1;

       }

     }

 #endif

   }

   /* Allocate memory for the array aRegIdx[].  There is one entry in the

   ** array for each index associated with table being updated.  Fill in

   ** the value with a register number for indices that are to be used

   ** and with zero for unused indices.

   */

   for(nIdx=0, pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext, nIdx++){}

   if( nIdx>0 ){

     aRegIdx = sqlite3DbMallocRaw(db, sizeof(Index*) * nIdx );

     if( aRegIdx==0 ) goto update_cleanup;

   }

   for(j=0, pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext, j++){

     int reg;

     if( chngRowid ){

       reg = ++pParse->nMem;

     }else{

       reg = 0;

       for(i=0; i<pIdx->nColumn; i++){

         if( aXRef[pIdx->aiColumn[i]]>=0 ){

           reg = ++pParse->nMem;

           break;

         }

       }

     }

     aRegIdx[j] = reg;

   }

   /* Allocate a block of register used to store the change record

   ** sent to sqlite3GenerateConstraintChecks().  There are either

   ** one or two registers for holding the rowid.  One rowid register

   ** is used if chngRowid is false and two are used if chngRowid is

   ** true.  Following these are pTab->nCol register holding column

   ** data.

   */

   regOldRowid = regNewRowid = pParse->nMem + 1;

   pParse->nMem += pTab->nCol + 1;

   if( chngRowid ){

     regNewRowid++;

     pParse->nMem++;

   }

   regData = regNewRowid+1;

   /* Begin generating code.

   */

   v = sqlite3GetVdbe(pParse);

   if( v==0 ) goto update_cleanup;

   if( pParse->nested==0 ) sqlite3VdbeCountChanges(v);

   sqlite3BeginWriteOperation(pParse, 1, iDb);

 #ifndef SQLITE_OMIT_VIRTUALTABLE

   /* Virtual tables must be handled separately */

   if( IsVirtual(pTab) ){

     updateVirtualTable(pParse, pTabList, pTab, pChanges, pRowidExpr, aXRef,

                        pWhere);

     pWhere = 0;

     pTabList = 0;

     goto update_cleanup;

   }

 #endif

   /* Start the view context

   */

   if( isView ){

     sqlite3AuthContextPush(pParse, &sContext, pTab->zName);

   }

   /* Generate the code for triggers.

   */

   if( triggers_exist ){

     int iGoto;

     /* Create pseudo-tables for NEW and OLD

     */

     sqlite3VdbeAddOp2(v, OP_SetNumColumns, 0, pTab->nCol);

     sqlite3VdbeAddOp2(v, OP_OpenPseudo, oldIdx, 0);

     sqlite3VdbeAddOp2(v, OP_SetNumColumns, 0, pTab->nCol);

     sqlite3VdbeAddOp2(v, OP_OpenPseudo, newIdx, 0);

     iGoto = sqlite3VdbeAddOp2(v, OP_Goto, 0, 0);

     addr = sqlite3VdbeMakeLabel(v);

     iBeginBeforeTrigger = sqlite3VdbeCurrentAddr(v);

     if( sqlite3CodeRowTrigger(pParse, TK_UPDATE, pChanges, TRIGGER_BEFORE, pTab,

           newIdx, oldIdx, onError, addr, &old_col_mask, &new_col_mask) ){

       goto update_cleanup;

     }

     iEndBeforeTrigger = sqlite3VdbeAddOp2(v, OP_Goto, 0, 0);

     iBeginAfterTrigger = sqlite3VdbeCurrentAddr(v);

     if( sqlite3CodeRowTrigger(pParse, TK_UPDATE, pChanges, TRIGGER_AFTER, pTab, 

           newIdx, oldIdx, onError, addr, &old_col_mask, &new_col_mask) ){

       goto update_cleanup;

     }

     iEndAfterTrigger = sqlite3VdbeAddOp2(v, OP_Goto, 0, 0);

     sqlite3VdbeJumpHere(v, iGoto);

   }

   /* If we are trying to update a view, realize that view into

   ** a ephemeral table.

   */

 #if !defined(SQLITE_OMIT_VIEW) && !defined(SQLITE_OMIT_TRIGGER)

   if( isView ){

     sqlite3MaterializeView(pParse, pTab, pWhere, iCur);

   }

 #endif

   /* Resolve the column names in all the expressions in the

   ** WHERE clause.

   */

   if( sqlite3ResolveExprNames(&sNC, pWhere) ){

     goto update_cleanup;

   }

   /* Begin the database scan

   */

   sqlite3VdbeAddOp2(v, OP_Null, 0, regOldRowid);

   pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, 0,

                              WHERE_ONEPASS_DESIRED);

   if( pWInfo==0 ) goto update_cleanup;

   okOnePass = pWInfo->okOnePass;

   /* Remember the rowid of every item to be updated.

   */

   sqlite3VdbeAddOp2(v, IsVirtual(pTab)?OP_VRowid:OP_Rowid, iCur, regOldRowid);

   if( !okOnePass ) sqlite3VdbeAddOp2(v, OP_FifoWrite, regOldRowid, 0);

   /* End the database scan loop.

   */

   sqlite3WhereEnd(pWInfo);

   /* Initialize the count of updated rows

   */

   if( db->flags & SQLITE_CountRows && !pParse->trigStack ){

     regRowCount = ++pParse->nMem;

     sqlite3VdbeAddOp2(v, OP_Integer, 0, regRowCount);

   }

   if( !isView && !IsVirtual(pTab) ){

     /* 

     ** Open every index that needs updating.  Note that if any

     ** index could potentially invoke a REPLACE conflict resolution 

     ** action, then we need to open all indices because we might need

     ** to be deleting some records.

     */

     if( !okOnePass ) sqlite3OpenTable(pParse, iCur, iDb, pTab, OP_OpenWrite); 

     if( onError==OE_Replace ){

       openAll = 1;

     }else{

       openAll = 0;

       for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){

         if( pIdx->onError==OE_Replace ){

           openAll = 1;

           break;

         }

       }

     }

     for(i=0, pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext, i++){

       if( openAll || aRegIdx[i]>0 ){

         KeyInfo *pKey = sqlite3IndexKeyinfo(pParse, pIdx);

         sqlite3VdbeAddOp4(v, OP_OpenWrite, iCur+i+1, pIdx->tnum, iDb,

                        (char*)pKey, P4_KEYINFO_HANDOFF);

         assert( pParse->nTab>iCur+i+1 );

       }

     }

   }

   /* Jump back to this point if a trigger encounters an IGNORE constraint. */

   if( triggers_exist ){

     sqlite3VdbeResolveLabel(v, addr);

   }

   /* Top of the update loop */

   if( okOnePass ){

     int a1 = sqlite3VdbeAddOp1(v, OP_NotNull, regOldRowid);

     addr = sqlite3VdbeAddOp0(v, OP_Goto);

     sqlite3VdbeJumpHere(v, a1);

   }else{

     addr = sqlite3VdbeAddOp2(v, OP_FifoRead, regOldRowid, 0);

   }

   if( triggers_exist ){

     int regRowid;

     int regRow;

     int regCols;

     /* Make cursor iCur point to the record that is being updated.

     */

     sqlite3VdbeAddOp3(v, OP_NotExists, iCur, addr, regOldRowid);

     /* Generate the OLD table

     */

     regRowid = sqlite3GetTempReg(pParse);

     regRow = sqlite3GetTempReg(pParse);

     sqlite3VdbeAddOp2(v, OP_Rowid, iCur, regRowid);

     if( !old_col_mask ){

       sqlite3VdbeAddOp2(v, OP_Null, 0, regRow);

     }else{

       sqlite3VdbeAddOp2(v, OP_RowData, iCur, regRow);

     }

     sqlite3VdbeAddOp3(v, OP_Insert, oldIdx, regRow, regRowid);

     /* Generate the NEW table

     */

     if( chngRowid ){

       sqlite3ExprCodeAndCache(pParse, pRowidExpr, regRowid);

       sqlite3VdbeAddOp1(v, OP_MustBeInt, regRowid);

     }else{

       sqlite3VdbeAddOp2(v, OP_Rowid, iCur, regRowid);

     }

     regCols = sqlite3GetTempRange(pParse, pTab->nCol);

     for(i=0; i<pTab->nCol; i++){

       if( i==pTab->iPKey ){

         sqlite3VdbeAddOp2(v, OP_Null, 0, regCols+i);

         continue;

       }

       j = aXRef[i];

       if( new_col_mask&((u32)1<<i) || new_col_mask==0xffffffff ){

         if( j<0 ){

           sqlite3VdbeAddOp3(v, OP_Column, iCur, i, regCols+i);

           sqlite3ColumnDefault(v, pTab, i);

         }else{

           sqlite3ExprCodeAndCache(pParse, pChanges->a[j].pExpr, regCols+i);

         }

       }else{

         sqlite3VdbeAddOp2(v, OP_Null, 0, regCols+i);

       }

     }

     sqlite3VdbeAddOp3(v, OP_MakeRecord, regCols, pTab->nCol, regRow);

     if( !isView ){

       sqlite3TableAffinityStr(v, pTab);

       sqlite3ExprCacheAffinityChange(pParse, regCols, pTab->nCol);

     }

     sqlite3ReleaseTempRange(pParse, regCols, pTab->nCol);

     /* if( pParse->nErr ) goto update_cleanup; */

     sqlite3VdbeAddOp3(v, OP_Insert, newIdx, regRow, regRowid);

     sqlite3ReleaseTempReg(pParse, regRowid);

     sqlite3ReleaseTempReg(pParse, regRow);

     sqlite3VdbeAddOp2(v, OP_Goto, 0, iBeginBeforeTrigger);

     sqlite3VdbeJumpHere(v, iEndBeforeTrigger);

   }

   if( !isView && !IsVirtual(pTab) ){

     /* Loop over every record that needs updating.  We have to load

     ** the old data for each record to be updated because some columns

     ** might not change and we will need to copy the old value.

     ** Also, the old data is needed to delete the old index entries.

     ** So make the cursor point at the old record.

     */

     sqlite3VdbeAddOp3(v, OP_NotExists, iCur, addr, regOldRowid);

     /* If the record number will change, push the record number as it

     ** will be after the update. (The old record number is currently

     ** on top of the stack.)

     */

     if( chngRowid ){

       sqlite3ExprCode(pParse, pRowidExpr, regNewRowid);

       sqlite3VdbeAddOp1(v, OP_MustBeInt, regNewRowid);

     }

     /* Compute new data for this record.  

     */

     for(i=0; i<pTab->nCol; i++){

       if( i==pTab->iPKey ){

         sqlite3VdbeAddOp2(v, OP_Null, 0, regData+i);

         continue;

       }

       j = aXRef[i];

       if( j<0 ){

         sqlite3VdbeAddOp3(v, OP_Column, iCur, i, regData+i);

         sqlite3ColumnDefault(v, pTab, i);

       }else{

         sqlite3ExprCode(pParse, pChanges->a[j].pExpr, regData+i);

       }

     }

     /* Do constraint checks

     */

     sqlite3GenerateConstraintChecks(pParse, pTab, iCur, regNewRowid,

                                     aRegIdx, chngRowid, 1,

                                     onError, addr);

     /* Delete the old indices for the current record.

     */

     j1 = sqlite3VdbeAddOp3(v, OP_NotExists, iCur, 0, regOldRowid);

     sqlite3GenerateRowIndexDelete(pParse, pTab, iCur, aRegIdx);

     /* If changing the record number, delete the old record.

     */

     if( chngRowid ){

       sqlite3VdbeAddOp2(v, OP_Delete, iCur, 0);

     }

     sqlite3VdbeJumpHere(v, j1);

     /* Create the new index entries and the new record.

     */

     sqlite3CompleteInsertion(pParse, pTab, iCur, regNewRowid, 

                              aRegIdx, chngRowid, 1, -1, 0);

   }

   /* Increment the row counter 

   */

   if( db->flags & SQLITE_CountRows && !pParse->trigStack){

     sqlite3VdbeAddOp2(v, OP_AddImm, regRowCount, 1);

   }

   /* If there are triggers, close all the cursors after each iteration

   ** through the loop.  The fire the after triggers.

   */

   if( triggers_exist ){

     sqlite3VdbeAddOp2(v, OP_Goto, 0, iBeginAfterTrigger);

     sqlite3VdbeJumpHere(v, iEndAfterTrigger);

   }

   /* Repeat the above with the next record to be updated, until

   ** all record selected by the WHERE clause have been updated.

   */

   sqlite3VdbeAddOp2(v, OP_Goto, 0, addr);

   sqlite3VdbeJumpHere(v, addr);

   /* Close all tables */

   for(i=0, pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext, i++){

     if( openAll || aRegIdx[i]>0 ){

       sqlite3VdbeAddOp2(v, OP_Close, iCur+i+1, 0);

     }

   }

   sqlite3VdbeAddOp2(v, OP_Close, iCur, 0);

   if( triggers_exist ){

     sqlite3VdbeAddOp2(v, OP_Close, newIdx, 0);

     sqlite3VdbeAddOp2(v, OP_Close, oldIdx, 0);

   }

   /*

   ** Return the number of rows that were changed. If this routine is 

   ** generating code because of a call to sqlite3NestedParse(), do not

   ** invoke the callback function.

   */

   if( db->flags & SQLITE_CountRows && !pParse->trigStack && pParse->nested==0 ){

     sqlite3VdbeAddOp2(v, OP_ResultRow, regRowCount, 1);

     sqlite3VdbeSetNumCols(v, 1);

     sqlite3VdbeSetColName(v, 0, COLNAME_NAME, "rows updated", P4_STATIC);

   }

 update_cleanup:

   sqlite3AuthContextPop(&sContext);

   sqlite3DbFree(db, aRegIdx);

   sqlite3DbFree(db, aXRef);

   sqlite3SrcListDelete(db, pTabList);

   sqlite3ExprListDelete(db, pChanges);

   sqlite3ExprDelete(db, pWhere);

   return;

 }

 #ifndef SQLITE_OMIT_VIRTUALTABLE

 /*

 ** Generate code for an UPDATE of a virtual table.

 **

 ** The strategy is that we create an ephemerial table that contains

 ** for each row to be changed:

 **

 **   (A)  The original rowid of that row.

 **   (B)  The revised rowid for the row. (note1)

 **   (C)  The content of every column in the row.

 **

 ** Then we loop over this ephemeral table and for each row in

 ** the ephermeral table call VUpdate.

 **

 ** When finished, drop the ephemeral table.

 **

 ** (note1) Actually, if we know in advance that (A) is always the same

 ** as (B) we only store (A), then duplicate (A) when pulling

 ** it out of the ephemeral table before calling VUpdate.

 */

 static void updateVirtualTable(

   Parse *pParse,       /* The parsing context */

   SrcList *pSrc,       /* The virtual table to be modified */

   Table *pTab,         /* The virtual table */

   ExprList *pChanges,  /* The columns to change in the UPDATE statement */

   Expr *pRowid,        /* Expression used to recompute the rowid */

   int *aXRef,          /* Mapping from columns of pTab to entries in pChanges */

   Expr *pWhere         /* WHERE clause of the UPDATE statement */

 ){

   Vdbe *v = pParse->pVdbe;  /* Virtual machine under construction */

   ExprList *pEList = 0;     /* The result set of the SELECT statement */

   Select *pSelect = 0;      /* The SELECT statement */

   Expr *pExpr;              /* Temporary expression */

   int ephemTab;             /* Table holding the result of the SELECT */

   int i;                    /* Loop counter */

   int addr;                 /* Address of top of loop */

   int iReg;                 /* First register in set passed to OP_VUpdate */

   sqlite3 *db = pParse->db; /* Database connection */

   const char *pVtab = (const char*)pTab->pVtab;

   SelectDest dest;

   /* Construct the SELECT statement that will find the new values for

   ** all updated rows. 

   */

   pEList = sqlite3ExprListAppend(pParse, 0, 

                                  sqlite3CreateIdExpr(pParse, "_rowid_"), 0);

   if( pRowid ){

     pEList = sqlite3ExprListAppend(pParse, pEList,

                                    sqlite3ExprDup(db, pRowid), 0);

   }

   assert( pTab->iPKey<0 );

   for(i=0; i<pTab->nCol; i++){

     if( aXRef[i]>=0 ){

       pExpr = sqlite3ExprDup(db, pChanges->a[aXRef[i]].pExpr);

     }else{

       pExpr = sqlite3CreateIdExpr(pParse, pTab->aCol[i].zName);

     }

     pEList = sqlite3ExprListAppend(pParse, pEList, pExpr, 0);

   }

   pSelect = sqlite3SelectNew(pParse, pEList, pSrc, pWhere, 0, 0, 0, 0, 0, 0);

   /* Create the ephemeral table into which the update results will

   ** be stored.

   */

   assert( v );

   ephemTab = pParse->nTab++;

   sqlite3VdbeAddOp2(v, OP_OpenEphemeral, ephemTab, pTab->nCol+1+(pRowid!=0));

   /* fill the ephemeral table 

   */

   sqlite3SelectDestInit(&dest, SRT_Table, ephemTab);

   sqlite3Select(pParse, pSelect, &dest);

   /* Generate code to scan the ephemeral table and call VUpdate. */

   iReg = ++pParse->nMem;

   pParse->nMem += pTab->nCol+1;

   sqlite3VdbeAddOp2(v, OP_Rewind, ephemTab, 0);

   addr = sqlite3VdbeCurrentAddr(v);

   sqlite3VdbeAddOp3(v, OP_Column,  ephemTab, 0, iReg);

   sqlite3VdbeAddOp3(v, OP_Column, ephemTab, (pRowid?1:0), iReg+1);

   for(i=0; i<pTab->nCol; i++){

     sqlite3VdbeAddOp3(v, OP_Column, ephemTab, i+1+(pRowid!=0), iReg+2+i);

   }

   sqlite3VtabMakeWritable(pParse, pTab);

   sqlite3VdbeAddOp4(v, OP_VUpdate, 0, pTab->nCol+2, iReg, pVtab, P4_VTAB);

   sqlite3VdbeAddOp2(v, OP_Next, ephemTab, addr);

   sqlite3VdbeJumpHere(v, addr-1);

   sqlite3VdbeAddOp2(v, OP_Close, ephemTab, 0);

   /* Cleanup */

   sqlite3SelectDelete(db, pSelect);  

 }

 #endif /* SQLITE_OMIT_VIRTUALTABLE */

 /* Make sure "isView" gets undefined in case this file becomes part of

 ** the amalgamation - so that subsequent files do not see isView as a

 ** macro. */

 #undef isView