/*

** 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 1.184 2008/09/01 21:59:43 shane 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);

    }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