SQLite

    pVTab = sqlite3GetVTable(db, pTab);
    if( pVTab->pVtab->pModule->xRename==0 ){
      pVTab = 0;
    }
  }
#endif

  /* Begin a transaction and code the VerifyCookie for database iDb. 
  ** Then modify the schema cookie (since the ALTER TABLE modifies the
  ** schema). Open a statement transaction if the table is a virtual
  ** table.
  */
  v = sqlite3GetVdbe(pParse);
  if( v==0 ){
    goto exit_rename_table;

    if( pParse->cookieGoto>0 ){
      yDbMask mask;
      int iDb, i, addr;
      sqlite3VdbeJumpHere(v, pParse->cookieGoto-1);
      for(iDb=0, mask=1; iDb<db->nDb; mask<<=1, iDb++){
        if( (mask & pParse->cookieMask)==0 ) continue;
        sqlite3VdbeUsesBtree(v, iDb);
        sqlite3VdbeAddOp2(v,OP_Transaction, iDb, (mask & pParse->writeMask)!=0);
        if( db->init.busy==0 ){
          assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
          sqlite3VdbeAddOp3(v, OP_VerifyCookie,



                            iDb, pParse->cookieValue[iDb],
                            db->aDb[iDb].pSchema->iGeneration);
        }


      }
#ifndef SQLITE_OMIT_VIRTUALTABLE
      for(i=0; i<pParse->nVtabLock; i++){
        char *vtab = (char *)sqlite3GetVTable(db, pParse->apVtabLock[i]);
        sqlite3VdbeAddOp4(v, OP_VBegin, 0, 0, 0, vtab, P4_VTAB);
      }
      pParse->nVtabLock = 0;

    assert( p->pEList!=0 );             /* Because of isCandidateForInOpt(p) */
    assert( p->pEList->a[0].pExpr!=0 ); /* Because of isCandidateForInOpt(p) */
    assert( p->pSrc!=0 );               /* Because of isCandidateForInOpt(p) */
    pTab = p->pSrc->a[0].pTab;
    pExpr = p->pEList->a[0].pExpr;
    iCol = (i16)pExpr->iColumn;
   
    /* Code an OP_VerifyCookie and OP_TableLock for <table>. */
    iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
    sqlite3CodeVerifySchema(pParse, iDb);
    sqlite3TableLock(pParse, iDb, pTab->tnum, 0, pTab->zName);

    /* This function is only called from two places. In both cases the vdbe
    ** has already been allocated. So assume sqlite3GetVdbe() is always
    ** successful here.

                   "cannot commit - no transaction is active"));
         
    rc = SQLITE_ERROR;
  }
  break;
}

/* Opcode: Transaction P1 P2 * * *
**
** Begin a transaction.  The transaction ends when a Commit or Rollback
** opcode is encountered.  Depending on the ON CONFLICT setting, the
** transaction might also be rolled back if an error is encountered.
**
** P1 is the index of the database file on which the transaction is
** started.  Index 0 is the main database file and index 1 is the

** connection is currently not in autocommit mode, or if there are other
** active statements. A statement transaction allows the changes made by this
** VDBE to be rolled back after an error without having to roll back the
** entire transaction. If no error is encountered, the statement transaction
** will automatically commit when the VDBE halts.
**
** If P2 is zero, then a read-lock is obtained on the database file.






*/
case OP_Transaction: {
  Btree *pBt;



  assert( p->bIsReader );
  assert( p->readOnly==0 || pOp->p2==0 );
  assert( pOp->p1>=0 && pOp->p1<db->nDb );
  assert( (p->btreeMask & (((yDbMask)1)<<pOp->p1))!=0 );
  if( pOp->p2 && (db->flags & SQLITE_QueryOnly)!=0 ){
    rc = SQLITE_READONLY;

      /* Store the current value of the database handles deferred constraint
      ** counter. If the statement transaction needs to be rolled back,
      ** the value of this counter needs to be restored too.  */
      p->nStmtDefCons = db->nDeferredCons;
      p->nStmtDefImmCons = db->nDeferredImmCons;
    }





























  }
  break;
}

/* Opcode: ReadCookie P1 P2 P3 * *
**
** Read cookie number P3 from database P1 and write it into register P2.

  }
  if( pOp->p1==1 ){
    /* Invalidate all prepared statements whenever the TEMP database
    ** schema is changed.  Ticket #1644 */
    sqlite3ExpirePreparedStatements(db);
    p->expired = 0;
  }
  break;
}

/* Opcode: VerifyCookie P1 P2 P3 * *
**
** Check the value of global database parameter number 0 (the
** schema version) and make sure it is equal to P2 and that the
** generation counter on the local schema parse equals P3.
**
** P1 is the database number which is 0 for the main database file
** and 1 for the file holding temporary tables and some higher number
** for auxiliary databases.
**
** The cookie changes its value whenever the database schema changes.
** This operation is used to detect when that the cookie has changed
** and that the current process needs to reread the schema.
**
** Either a transaction needs to have been started or an OP_Open needs
** to be executed (to establish a read lock) before this opcode is
** invoked.
*/
case OP_VerifyCookie: {
  int iMeta;
  int iGen;
  Btree *pBt;

  assert( pOp->p1>=0 && pOp->p1<db->nDb );
  assert( (p->btreeMask & (((yDbMask)1)<<pOp->p1))!=0 );
  assert( sqlite3SchemaMutexHeld(db, pOp->p1, 0) );
  assert( p->bIsReader );
  pBt = db->aDb[pOp->p1].pBt;
  if( pBt ){
    sqlite3BtreeGetMeta(pBt, BTREE_SCHEMA_VERSION, (u32 *)&iMeta);
    iGen = db->aDb[pOp->p1].pSchema->iGeneration;
  }else{
    iGen = iMeta = 0;
  }
  if( iMeta!=pOp->p2 || iGen!=pOp->p3 ){
    sqlite3DbFree(db, p->zErrMsg);
    p->zErrMsg = sqlite3DbStrDup(db, "database schema has changed");
    /* If the schema-cookie from the database file matches the cookie 
    ** stored with the in-memory representation of the schema, do
    ** not reload the schema from the database file.
    **
    ** If virtual-tables are in use, this is not just an optimization.
    ** Often, v-tables store their data in other SQLite tables, which
    ** are queried from within xNext() and other v-table methods using
    ** prepared queries. If such a query is out-of-date, we do not want to
    ** discard the database schema, as the user code implementing the
    ** v-table would have to be ready for the sqlite3_vtab structure itself
    ** to be invalidated whenever sqlite3_step() is called from within 
    ** a v-table method.
    */
    if( db->aDb[pOp->p1].pSchema->schema_cookie!=iMeta ){
      sqlite3ResetOneSchema(db, pOp->p1);
    }

    p->expired = 1;
    rc = SQLITE_SCHEMA;
  }
  break;
}

/* Opcode: OpenRead P1 P2 P3 P4 P5
** Synopsis: root=P2 iDb=P3
**
** Open a read-only cursor for the database table whose root page is

  ** blob_bytes() functions.
  **
  ** The sqlite3_blob_close() function finalizes the vdbe program,
  ** which closes the b-tree cursor and (possibly) commits the 
  ** transaction.
  */
  static const VdbeOpList openBlob[] = {
    {OP_Transaction, 0, 0, 0},     /* 0: Start a transaction */
    {OP_VerifyCookie, 0, 0, 0},    /* 1: Check the schema cookie */
    {OP_TableLock, 0, 0, 0},       /* 2: Acquire a read or write lock */

    /* One of the following two instructions is replaced by an OP_Noop. */
    {OP_OpenRead, 0, 0, 0},        /* 3: Open cursor 0 for reading */
    {OP_OpenWrite, 0, 0, 0},       /* 4: Open cursor 0 for read/write */

    {OP_Variable, 1, 1, 1},        /* 5: Push the rowid to the stack */
    {OP_NotExists, 0, 10, 1},      /* 6: Seek the cursor */
    {OP_Column, 0, 0, 1},          /* 7  */
    {OP_ResultRow, 1, 0, 0},       /* 8  */
    {OP_Goto, 0, 5, 0},            /* 9  */
    {OP_Close, 0, 0, 0},           /* 10 */
    {OP_Halt, 0, 0, 0},            /* 11 */
  };

  int rc = SQLITE_OK;
  char *zErr = 0;
  Table *pTab;
  Parse *pParse = 0;
  Incrblob *pBlob = 0;

    pBlob->pStmt = (sqlite3_stmt *)sqlite3VdbeCreate(pParse);
    assert( pBlob->pStmt || db->mallocFailed );
    if( pBlob->pStmt ){
      Vdbe *v = (Vdbe *)pBlob->pStmt;
      int iDb = sqlite3SchemaToIndex(db, pTab->pSchema);

      sqlite3VdbeAddOpList(v, sizeof(openBlob)/sizeof(VdbeOpList), openBlob);


      /* Configure the OP_Transaction */
      sqlite3VdbeChangeP1(v, 0, iDb);
      sqlite3VdbeChangeP2(v, 0, flags);

      /* Configure the OP_VerifyCookie */

      sqlite3VdbeChangeP1(v, 1, iDb);
      sqlite3VdbeChangeP2(v, 1, pTab->pSchema->schema_cookie);
      sqlite3VdbeChangeP3(v, 1, pTab->pSchema->iGeneration);

      /* Make sure a mutex is held on the table to be accessed */
      sqlite3VdbeUsesBtree(v, iDb); 

      /* Configure the OP_TableLock instruction */
#ifdef SQLITE_OMIT_SHARED_CACHE
      sqlite3VdbeChangeToNoop(v, 2);
#else
      sqlite3VdbeChangeP1(v, 2, iDb);
      sqlite3VdbeChangeP2(v, 2, pTab->tnum);
      sqlite3VdbeChangeP3(v, 2, flags);
      sqlite3VdbeChangeP4(v, 2, pTab->zName, P4_TRANSIENT);
#endif

      /* Remove either the OP_OpenWrite or OpenRead. Set the P2 
      ** parameter of the other to pTab->tnum.  */
      sqlite3VdbeChangeToNoop(v, 4 - flags);
      sqlite3VdbeChangeP2(v, 3 + flags, pTab->tnum);
      sqlite3VdbeChangeP3(v, 3 + flags, iDb);

      /* Configure the number of columns. Configure the cursor to
      ** think that the table has one more column than it really
      ** does. An OP_Column to retrieve this imaginary column will
      ** always return an SQL NULL. This is useful because it means
      ** we can invoke OP_Column to fill in the vdbe cursors type 
      ** and offset cache without causing any IO.
      */
      sqlite3VdbeChangeP4(v, 3+flags, SQLITE_INT_TO_PTR(pTab->nCol+1),P4_INT32);
      sqlite3VdbeChangeP2(v, 7, pTab->nCol);
      if( !db->mallocFailed ){
        pParse->nVar = 1;
        pParse->nMem = 1;
        pParse->nTab = 1;
        sqlite3VdbeMakeReady(v, pParse);
      }
    }