**    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 used to generate VDBE code
** that implements the ALTER TABLE command.
**
** $Id: alter.c,v 1.57 2009/04/16 16:30:18 drh Exp $
*/
#include "sqliteInt.h"

/*
** The code in this file only exists if we are not omitting the
** ALTER TABLE logic from the build.
*/
................................................................................
  reloadTableSchema(pParse, pTab, zName);

exit_rename_table:
  sqlite3SrcListDelete(db, pSrc);
  sqlite3DbFree(db, zName);
}



























/*
** This function is called after an "ALTER TABLE ... ADD" statement
** has been parsed. Argument pColDef contains the text of the new
** column definition.
**
** The Table structure pParse->pNewTable was extended to include

**    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 used to generate VDBE code
** that implements the ALTER TABLE command.
**
** $Id: alter.c,v 1.58 2009/05/12 17:46:54 drh Exp $
*/
#include "sqliteInt.h"

/*
** The code in this file only exists if we are not omitting the
** ALTER TABLE logic from the build.
*/
................................................................................
  reloadTableSchema(pParse, pTab, zName);

exit_rename_table:
  sqlite3SrcListDelete(db, pSrc);
  sqlite3DbFree(db, zName);
}


/*
** Generate code to make sure the file format number is at least minFormat.
** The generated code will increase the file format number if necessary.
*/
void sqlite3MinimumFileFormat(Parse *pParse, int iDb, int minFormat){
  Vdbe *v;
  v = sqlite3GetVdbe(pParse);
  /* The VDBE should have been allocated before this routine is called.
  ** If that allocation failed, we would have quit before reaching this
  ** point */
  if( ALWAYS(v) ){
    int r1 = sqlite3GetTempReg(pParse);
    int r2 = sqlite3GetTempReg(pParse);
    int j1;
    sqlite3VdbeAddOp3(v, OP_ReadCookie, iDb, r1, 1);
    sqlite3VdbeUsesBtree(v, iDb);
    sqlite3VdbeAddOp2(v, OP_Integer, minFormat, r2);
    j1 = sqlite3VdbeAddOp3(v, OP_Ge, r2, 0, r1);
    sqlite3VdbeAddOp3(v, OP_SetCookie, iDb, 1, r2);
    sqlite3VdbeJumpHere(v, j1);
    sqlite3ReleaseTempReg(pParse, r1);
    sqlite3ReleaseTempReg(pParse, r2);
  }
}

/*
** This function is called after an "ALTER TABLE ... ADD" statement
** has been parsed. Argument pColDef contains the text of the new
** column definition.
**
** The Table structure pParse->pNewTable was extended to include

**     CREATE INDEX
**     DROP INDEX
**     creating ID lists
**     BEGIN TRANSACTION
**     COMMIT
**     ROLLBACK
**
** $Id: build.c,v 1.539 2009/05/12 00:40:13 drh Exp $
*/
#include "sqliteInt.h"

/*
** This routine is called when a new SQL statement is beginning to
** be parsed.  Initialize the pParse structure as needed.
*/
................................................................................
  Table *p = pParse->pNewTable;
  int nByte;
  int i;
  int nCol;
  char *z;

  assert( pTo!=0 );
  if( p==0 || pParse->nErr || IN_DECLARE_VTAB ) goto fk_end;
  if( pFromCol==0 ){
    int iCol = p->nCol-1;
    if( iCol<0 ) goto fk_end;
    if( pToCol && pToCol->nExpr!=1 ){
      sqlite3ErrorMsg(pParse, "foreign key on %s"
         " should reference only one column of table %T",
         p->aCol[iCol].zName, pTo);
      goto fk_end;
    }
    nCol = 1;
................................................................................
  int iDb;             /* Index of the database that is being written */
  Token *pName = 0;    /* Unqualified name of the index to create */
  struct ExprList_item *pListItem; /* For looping over pList */
  int nCol;
  int nExtra = 0;
  char *zExtra;


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



    goto exit_create_index;
  }

  /*
  ** Find the table that is to be indexed.  Return early if not found.
  */
  if( pTblName!=0 ){
................................................................................
#ifndef SQLITE_OMIT_TEMPDB
    /* If the index name was unqualified, check if the the table
    ** is a temp table. If so, set the database to 1. Do not do this
    ** if initialising a database schema.
    */
    if( !db->init.busy ){
      pTab = sqlite3SrcListLookup(pParse, pTblName);
      if( pName2 && pName2->n==0 && pTab && pTab->pSchema==db->aDb[1].pSchema ){
        iDb = 1;
      }
    }
#endif

    if( sqlite3FixInit(&sFix, pParse, iDb, "index", pName) &&
        sqlite3FixSrcList(&sFix, pTblName)
................................................................................
    assert( pName==0 );
    pTab = pParse->pNewTable;
    if( !pTab ) goto exit_create_index;
    iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
  }
  pDb = &db->aDb[iDb];

  if( pTab==0 || pParse->nErr ) goto exit_create_index;

  if( sqlite3StrNICmp(pTab->zName, "sqlite_", 7)==0 
       && memcmp(&pTab->zName[7],"altertab_",9)!=0 ){
    sqlite3ErrorMsg(pParse, "table %s may not be indexed", pTab->zName);
    goto exit_create_index;
  }
#ifndef SQLITE_OMIT_VIEW
  if( pTab->pSelect ){
................................................................................
  **
  ** If pName==0 it means that we are
  ** dealing with a primary key or UNIQUE constraint.  We have to invent our
  ** own name.
  */
  if( pName ){
    zName = sqlite3NameFromToken(db, pName);
    if( SQLITE_OK!=sqlite3ReadSchema(pParse) ) goto exit_create_index;
    if( zName==0 ) goto exit_create_index;
    if( SQLITE_OK!=sqlite3CheckObjectName(pParse, zName) ){
      goto exit_create_index;
    }
    if( !db->init.busy ){
      if( SQLITE_OK!=sqlite3ReadSchema(pParse) ) goto exit_create_index;
      if( sqlite3FindTable(db, zName, 0)!=0 ){
        sqlite3ErrorMsg(pParse, "there is already a table named %s", zName);
        goto exit_create_index;
      }
    }
    if( sqlite3FindIndex(db, zName, pDb->zName)!=0 ){
      if( !ifNotExist ){
................................................................................
    pList->a[0].sortOrder = (u8)sortOrder;
  }

  /* Figure out how many bytes of space are required to store explicitly
  ** specified collation sequence names.
  */
  for(i=0; i<pList->nExpr; i++){
    Expr *pExpr;

    CollSeq *pColl;
    if( (pExpr = pList->a[i].pExpr)!=0 && (pColl = pExpr->pColl)!=0 ){



      nExtra += (1 + sqlite3Strlen30(pColl->zName));

    }
  }

  /* 
  ** Allocate the index structure. 
  */
  nName = sqlite3Strlen30(zName);
................................................................................
  }else{
    sortOrderMask = 0;    /* Ignore DESC */
  }

  /* Scan the names of the columns of the table to be indexed and
  ** load the column indices into the Index structure.  Report an error
  ** if any column is not found.






  */
  for(i=0, pListItem=pList->a; i<pList->nExpr; i++, pListItem++){
    const char *zColName = pListItem->zName;
    Column *pTabCol;
    int requestedSortOrder;
    char *zColl;                   /* Collation sequence name */

................................................................................
      if( sqlite3StrICmp(zColName, pTabCol->zName)==0 ) break;
    }
    if( j>=pTab->nCol ){
      sqlite3ErrorMsg(pParse, "table %s has no column named %s",
        pTab->zName, zColName);
      goto exit_create_index;
    }
    /* TODO:  Add a test to make sure that the same column is not named
    ** more than once within the same index.  Only the first instance of
    ** the column will ever be used by the optimizer.  Note that using the
    ** same column more than once cannot be an error because that would 
    ** break backwards compatibility - it needs to be a warning.
    */
    pIndex->aiColumn[i] = j;
    if( pListItem->pExpr && pListItem->pExpr->pColl ){
      assert( pListItem->pExpr->pColl );
      zColl = zExtra;
      sqlite3_snprintf(nExtra, zExtra, "%s", pListItem->pExpr->pColl->zName);
      zExtra += (sqlite3Strlen30(zColl) + 1);



    }else{
      zColl = pTab->aCol[j].zColl;
      if( !zColl ){
        zColl = db->pDfltColl->zName;
      }
    }
    if( !db->init.busy && !sqlite3LocateCollSeq(pParse, zColl) ){
................................................................................
    ** CREATE TABLE t(x PRIMARY KEY, y);
    ** CREATE TABLE t(x, y, UNIQUE(x, y));
    **
    ** Either way, check to see if the table already has such an index. If
    ** so, don't bother creating this one. This only applies to
    ** automatically created indices. Users can do as they wish with
    ** explicit indices.








    */
    Index *pIdx;
    for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
      int k;
      assert( pIdx->onError!=OE_None );
      assert( pIdx->autoIndex );
      assert( pIndex->onError!=OE_None );

      if( pIdx->nColumn!=pIndex->nColumn ) continue;
      for(k=0; k<pIdx->nColumn; k++){
        const char *z1 = pIdx->azColl[k];
        const char *z2 = pIndex->azColl[k];
        if( pIdx->aiColumn[k]!=pIndex->aiColumn[k] ) break;
        if( pIdx->aSortOrder[k]!=pIndex->aSortOrder[k] ) break;

        if( z1!=z2 && sqlite3StrICmp(z1, z2) ) break;
      }
      if( k==pIdx->nColumn ){
        if( pIdx->onError!=pIndex->onError ){
          /* This constraint creates the same index as a previous
          ** constraint specified somewhere in the CREATE TABLE statement.
          ** However the ON CONFLICT clauses are different. If both this 
................................................................................
  ** we don't want to recreate it.
  **
  ** If pTblName==0 it means this index is generated as a primary key
  ** or UNIQUE constraint of a CREATE TABLE statement.  Since the table
  ** has just been created, it contains no data and the index initialization
  ** step can be skipped.
  */
  else if( db->init.busy==0 ){
    Vdbe *v;
    char *zStmt;
    int iMem = ++pParse->nMem;

    v = sqlite3GetVdbe(pParse);
    if( v==0 ) goto exit_create_index;

................................................................................
    */
    sqlite3BeginWriteOperation(pParse, 1, iDb);
    sqlite3VdbeAddOp2(v, OP_CreateIndex, iDb, iMem);

    /* Gather the complete text of the CREATE INDEX statement into
    ** the zStmt variable
    */
    if( pStart && pEnd ){

      /* A named index with an explicit CREATE INDEX statement */
      zStmt = sqlite3MPrintf(db, "CREATE%s INDEX %.*s",
        onError==OE_None ? "" : " UNIQUE",
        pEnd->z - pName->z + 1,
        pName->z);
    }else{
      /* An automatic index created by a PRIMARY KEY or UNIQUE constraint */
................................................................................
         sqlite3MPrintf(db, "name='%q'", pIndex->zName), P4_DYNAMIC);
      sqlite3VdbeAddOp1(v, OP_Expire, 0);
    }
  }

  /* When adding an index to the list of indices for a table, make
  ** sure all indices labeled OE_Replace come after all those labeled
  ** OE_Ignore.  This is necessary for the correct operation of UPDATE

  ** and INSERT.
  */
  if( db->init.busy || pTblName==0 ){
    if( onError!=OE_Replace || pTab->pIndex==0
         || pTab->pIndex->onError==OE_Replace){
      pIndex->pNext = pTab->pIndex;
      pTab->pIndex = pIndex;
    }else{
................................................................................
  }
  sqlite3ExprListDelete(db, pList);
  sqlite3SrcListDelete(db, pTblName);
  sqlite3DbFree(db, zName);
  return;
}

/*
** Generate code to make sure the file format number is at least minFormat.
** The generated code will increase the file format number if necessary.
*/
void sqlite3MinimumFileFormat(Parse *pParse, int iDb, int minFormat){
  Vdbe *v;
  v = sqlite3GetVdbe(pParse);
  if( v ){
    int r1 = sqlite3GetTempReg(pParse);
    int r2 = sqlite3GetTempReg(pParse);
    int j1;
    sqlite3VdbeAddOp3(v, OP_ReadCookie, iDb, r1, 1);
    sqlite3VdbeUsesBtree(v, iDb);
    sqlite3VdbeAddOp2(v, OP_Integer, minFormat, r2);
    j1 = sqlite3VdbeAddOp3(v, OP_Ge, r2, 0, r1);
    sqlite3VdbeAddOp3(v, OP_SetCookie, iDb, 1, r2);
    sqlite3VdbeJumpHere(v, j1);
    sqlite3ReleaseTempReg(pParse, r1);
    sqlite3ReleaseTempReg(pParse, r2);
  }
}

/*
** Fill the Index.aiRowEst[] array with default information - information
** to be used when we have not run the ANALYZE command.
**
** aiRowEst[0] is suppose to contain the number of elements in the index.
** Since we do not know, guess 1 million.  aiRowEst[1] is an estimate of the
** number of rows in the table that match any particular value of the
................................................................................
*/
void sqlite3DropIndex(Parse *pParse, SrcList *pName, int ifExists){
  Index *pIndex;
  Vdbe *v;
  sqlite3 *db = pParse->db;
  int iDb;

  if( pParse->nErr || db->mallocFailed ){
    goto exit_drop_index;
  }
  assert( pName->nSrc==1 );
  if( SQLITE_OK!=sqlite3ReadSchema(pParse) ){
    goto exit_drop_index;
  }
  pIndex = sqlite3FindIndex(db, pName->a[0].zName, pName->a[0].zDatabase);
................................................................................
**         sqlite3SrcListAppend(D,A,B,0);
**
** Then B is a table name and the database name is unspecified.  If called
** like this:
**
**         sqlite3SrcListAppend(D,A,B,C);
**
** Then C is the table name and B is the database name.



*/
SrcList *sqlite3SrcListAppend(
  sqlite3 *db,        /* Connection to notify of malloc failures */
  SrcList *pList,     /* Append to this SrcList. NULL creates a new SrcList */
  Token *pTable,      /* Table to append */
  Token *pDatabase    /* Database of the table */
){
  struct SrcList_item *pItem;

  if( pList==0 ){
    pList = sqlite3DbMallocZero(db, sizeof(SrcList) );
    if( pList==0 ) return 0;
    pList->nAlloc = 1;
  }
  pList = sqlite3SrcListEnlarge(db, pList, 1, pList->nSrc);
  if( db->mallocFailed ){
................................................................................
    sqlite3SrcListDelete(db, pList);
    return 0;
  }
  pItem = &pList->a[pList->nSrc-1];
  if( pDatabase && pDatabase->z==0 ){
    pDatabase = 0;
  }
  if( pDatabase && pTable ){
    Token *pTemp = pDatabase;
    pDatabase = pTable;
    pTable = pTemp;
  }
  pItem->zName = sqlite3NameFromToken(db, pTable);
  pItem->zDatabase = sqlite3NameFromToken(db, pDatabase);
  return pList;
................................................................................
** Begin a transaction
*/
void sqlite3BeginTransaction(Parse *pParse, int type){
  sqlite3 *db;
  Vdbe *v;
  int i;




  if( pParse==0 || (db=pParse->db)==0 || db->aDb[0].pBt==0 ) return;
  if( pParse->nErr || db->mallocFailed ) return;
  if( sqlite3AuthCheck(pParse, SQLITE_TRANSACTION, "BEGIN", 0, 0) ) return;


  v = sqlite3GetVdbe(pParse);
  if( !v ) return;
  if( type!=TK_DEFERRED ){
    for(i=0; i<db->nDb; i++){
      sqlite3VdbeAddOp2(v, OP_Transaction, i, (type==TK_EXCLUSIVE)+1);
      sqlite3VdbeUsesBtree(v, i);
    }
................................................................................
/*
** Commit a transaction
*/
void sqlite3CommitTransaction(Parse *pParse){
  sqlite3 *db;
  Vdbe *v;




  if( pParse==0 || (db=pParse->db)==0 || db->aDb[0].pBt==0 ) return;
  if( pParse->nErr || db->mallocFailed ) return;
  if( sqlite3AuthCheck(pParse, SQLITE_TRANSACTION, "COMMIT", 0, 0) ) return;


  v = sqlite3GetVdbe(pParse);
  if( v ){
    sqlite3VdbeAddOp2(v, OP_AutoCommit, 1, 0);
  }
}

/*
** Rollback a transaction
*/
void sqlite3RollbackTransaction(Parse *pParse){
  sqlite3 *db;
  Vdbe *v;




  if( pParse==0 || (db=pParse->db)==0 || db->aDb[0].pBt==0 ) return;
  if( pParse->nErr || db->mallocFailed ) return;
  if( sqlite3AuthCheck(pParse, SQLITE_TRANSACTION, "ROLLBACK", 0, 0) ) return;


  v = sqlite3GetVdbe(pParse);
  if( v ){
    sqlite3VdbeAddOp2(v, OP_AutoCommit, 1, 1);
  }
}

/*
................................................................................

  /* Read the database schema. If an error occurs, leave an error message
  ** and code in pParse and return NULL. */
  if( SQLITE_OK!=sqlite3ReadSchema(pParse) ){
    return;
  }

  if( pName1==0 || pName1->z==0 ){
    reindexDatabases(pParse, 0);
    return;
  }else if( pName2==0 || pName2->z==0 ){
    char *zColl;
    assert( pName1->z );
    zColl = sqlite3NameFromToken(pParse->db, pName1);
    if( !zColl ) return;
    pColl = sqlite3FindCollSeq(db, ENC(db), zColl, 0);
    if( pColl ){
      if( zColl ){
        reindexDatabases(pParse, zColl);
        sqlite3DbFree(db, zColl);
      }
      return;
    }
    sqlite3DbFree(db, zColl);
  }
  iDb = sqlite3TwoPartName(pParse, pName1, pName2, &pObjName);
  if( iDb<0 ) return;
  z = sqlite3NameFromToken(db, pObjName);

**     CREATE INDEX
**     DROP INDEX
**     creating ID lists
**     BEGIN TRANSACTION
**     COMMIT
**     ROLLBACK
**
** $Id: build.c,v 1.540 2009/05/12 17:46:54 drh Exp $
*/
#include "sqliteInt.h"

/*
** This routine is called when a new SQL statement is beginning to
** be parsed.  Initialize the pParse structure as needed.
*/
................................................................................
  Table *p = pParse->pNewTable;
  int nByte;
  int i;
  int nCol;
  char *z;

  assert( pTo!=0 );
  if( p==0 || NEVER(pParse->nErr) || IN_DECLARE_VTAB ) goto fk_end;
  if( pFromCol==0 ){
    int iCol = p->nCol-1;
    if( NEVER(iCol<0) ) goto fk_end;
    if( pToCol && pToCol->nExpr!=1 ){
      sqlite3ErrorMsg(pParse, "foreign key on %s"
         " should reference only one column of table %T",
         p->aCol[iCol].zName, pTo);
      goto fk_end;
    }
    nCol = 1;
................................................................................
  int iDb;             /* Index of the database that is being written */
  Token *pName = 0;    /* Unqualified name of the index to create */
  struct ExprList_item *pListItem; /* For looping over pList */
  int nCol;
  int nExtra = 0;
  char *zExtra;

  assert( pStart==0 || pEnd!=0 ); /* pEnd must be non-NULL if pStart is */
  if( NEVER(pParse->nErr>0) || db->mallocFailed || IN_DECLARE_VTAB ){
    goto exit_create_index;
  }
  if( SQLITE_OK!=sqlite3ReadSchema(pParse) ){
    goto exit_create_index;
  }

  /*
  ** Find the table that is to be indexed.  Return early if not found.
  */
  if( pTblName!=0 ){
................................................................................
#ifndef SQLITE_OMIT_TEMPDB
    /* If the index name was unqualified, check if the the table
    ** is a temp table. If so, set the database to 1. Do not do this
    ** if initialising a database schema.
    */
    if( !db->init.busy ){
      pTab = sqlite3SrcListLookup(pParse, pTblName);
      if( pName2->n==0 && pTab && pTab->pSchema==db->aDb[1].pSchema ){
        iDb = 1;
      }
    }
#endif

    if( sqlite3FixInit(&sFix, pParse, iDb, "index", pName) &&
        sqlite3FixSrcList(&sFix, pTblName)
................................................................................
    assert( pName==0 );
    pTab = pParse->pNewTable;
    if( !pTab ) goto exit_create_index;
    iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
  }
  pDb = &db->aDb[iDb];

  assert( pTab!=0 );
  assert( pParse->nErr==0 );
  if( sqlite3StrNICmp(pTab->zName, "sqlite_", 7)==0 
       && memcmp(&pTab->zName[7],"altertab_",9)!=0 ){
    sqlite3ErrorMsg(pParse, "table %s may not be indexed", pTab->zName);
    goto exit_create_index;
  }
#ifndef SQLITE_OMIT_VIEW
  if( pTab->pSelect ){
................................................................................
  **
  ** If pName==0 it means that we are
  ** dealing with a primary key or UNIQUE constraint.  We have to invent our
  ** own name.
  */
  if( pName ){
    zName = sqlite3NameFromToken(db, pName);

    if( zName==0 ) goto exit_create_index;
    if( SQLITE_OK!=sqlite3CheckObjectName(pParse, zName) ){
      goto exit_create_index;
    }
    if( !db->init.busy ){

      if( sqlite3FindTable(db, zName, 0)!=0 ){
        sqlite3ErrorMsg(pParse, "there is already a table named %s", zName);
        goto exit_create_index;
      }
    }
    if( sqlite3FindIndex(db, zName, pDb->zName)!=0 ){
      if( !ifNotExist ){
................................................................................
    pList->a[0].sortOrder = (u8)sortOrder;
  }

  /* Figure out how many bytes of space are required to store explicitly
  ** specified collation sequence names.
  */
  for(i=0; i<pList->nExpr; i++){
    Expr *pExpr = pList->a[i].pExpr;
    if( pExpr ){
      CollSeq *pColl = pExpr->pColl;

      /* Either pColl!=0 or there was an OOM failure.  But if an OOM
      ** failure we have quit before reaching this point. */
      if( ALWAYS(pColl) ){
        nExtra += (1 + sqlite3Strlen30(pColl->zName));
      }
    }
  }

  /* 
  ** Allocate the index structure. 
  */
  nName = sqlite3Strlen30(zName);
................................................................................
  }else{
    sortOrderMask = 0;    /* Ignore DESC */
  }

  /* Scan the names of the columns of the table to be indexed and
  ** load the column indices into the Index structure.  Report an error
  ** if any column is not found.
  **
  ** TODO:  Add a test to make sure that the same column is not named
  ** more than once within the same index.  Only the first instance of
  ** the column will ever be used by the optimizer.  Note that using the
  ** same column more than once cannot be an error because that would 
  ** break backwards compatibility - it needs to be a warning.
  */
  for(i=0, pListItem=pList->a; i<pList->nExpr; i++, pListItem++){
    const char *zColName = pListItem->zName;
    Column *pTabCol;
    int requestedSortOrder;
    char *zColl;                   /* Collation sequence name */

................................................................................
      if( sqlite3StrICmp(zColName, pTabCol->zName)==0 ) break;
    }
    if( j>=pTab->nCol ){
      sqlite3ErrorMsg(pParse, "table %s has no column named %s",
        pTab->zName, zColName);
      goto exit_create_index;
    }
    pIndex->aiColumn[i] = j;
    /* Justification of the ALWAYS(pListItem->pExpr->pColl):  Because of
    ** the way the "idxlist" non-terminal is constructed by the parser,
    ** if pListItem->pExpr is not null then either pListItem->pExpr->pColl
    ** must exist or else there must have been an OOM error.  But if there
    ** was an OOM error, we would never reach this point. */
    if( pListItem->pExpr && ALWAYS(pListItem->pExpr->pColl) ){
      int nColl;
      zColl = pListItem->pExpr->pColl->zName;
      nColl = sqlite3Strlen30(zColl) + 1;
      assert( nExtra>=nColl );
      memcpy(zExtra, zColl, nColl);
      zColl = zExtra;
      zExtra += nColl;
      nExtra -= nColl;
    }else{
      zColl = pTab->aCol[j].zColl;
      if( !zColl ){
        zColl = db->pDfltColl->zName;
      }
    }
    if( !db->init.busy && !sqlite3LocateCollSeq(pParse, zColl) ){
................................................................................
    ** CREATE TABLE t(x PRIMARY KEY, y);
    ** CREATE TABLE t(x, y, UNIQUE(x, y));
    **
    ** Either way, check to see if the table already has such an index. If
    ** so, don't bother creating this one. This only applies to
    ** automatically created indices. Users can do as they wish with
    ** explicit indices.
    **
    ** Two UNIQUE or PRIMARY KEY constraints are considered equivalent
    ** (and thus suppressing the second one) even if they have different
    ** sort orders.
    **
    ** If there are different collating sequences or if the columns of
    ** the constraint occur in different orders, then the constraints are
    ** considered distinct and both result in separate indices.
    */
    Index *pIdx;
    for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
      int k;
      assert( pIdx->onError!=OE_None );
      assert( pIdx->autoIndex );
      assert( pIndex->onError!=OE_None );

      if( pIdx->nColumn!=pIndex->nColumn ) continue;
      for(k=0; k<pIdx->nColumn; k++){
        const char *z1;
        const char *z2;
        if( pIdx->aiColumn[k]!=pIndex->aiColumn[k] ) break;
        z1 = pIdx->azColl[k];
        z2 = pIndex->azColl[k];
        if( z1!=z2 && sqlite3StrICmp(z1, z2) ) break;
      }
      if( k==pIdx->nColumn ){
        if( pIdx->onError!=pIndex->onError ){
          /* This constraint creates the same index as a previous
          ** constraint specified somewhere in the CREATE TABLE statement.
          ** However the ON CONFLICT clauses are different. If both this 
................................................................................
  ** we don't want to recreate it.
  **
  ** If pTblName==0 it means this index is generated as a primary key
  ** or UNIQUE constraint of a CREATE TABLE statement.  Since the table
  ** has just been created, it contains no data and the index initialization
  ** step can be skipped.
  */
  else{ /* if( db->init.busy==0 ) */
    Vdbe *v;
    char *zStmt;
    int iMem = ++pParse->nMem;

    v = sqlite3GetVdbe(pParse);
    if( v==0 ) goto exit_create_index;

................................................................................
    */
    sqlite3BeginWriteOperation(pParse, 1, iDb);
    sqlite3VdbeAddOp2(v, OP_CreateIndex, iDb, iMem);

    /* Gather the complete text of the CREATE INDEX statement into
    ** the zStmt variable
    */
    if( pStart ){
      assert( pEnd!=0 );
      /* A named index with an explicit CREATE INDEX statement */
      zStmt = sqlite3MPrintf(db, "CREATE%s INDEX %.*s",
        onError==OE_None ? "" : " UNIQUE",
        pEnd->z - pName->z + 1,
        pName->z);
    }else{
      /* An automatic index created by a PRIMARY KEY or UNIQUE constraint */
................................................................................
         sqlite3MPrintf(db, "name='%q'", pIndex->zName), P4_DYNAMIC);
      sqlite3VdbeAddOp1(v, OP_Expire, 0);
    }
  }

  /* When adding an index to the list of indices for a table, make
  ** sure all indices labeled OE_Replace come after all those labeled
  ** OE_Ignore.  This is necessary for the correct constraint check
  ** processing (in sqlite3GenerateConstraintChecks()) as part of
  ** UPDATE and INSERT statements.  
  */
  if( db->init.busy || pTblName==0 ){
    if( onError!=OE_Replace || pTab->pIndex==0
         || pTab->pIndex->onError==OE_Replace){
      pIndex->pNext = pTab->pIndex;
      pTab->pIndex = pIndex;
    }else{
................................................................................
  }
  sqlite3ExprListDelete(db, pList);
  sqlite3SrcListDelete(db, pTblName);
  sqlite3DbFree(db, zName);
  return;
}























/*
** Fill the Index.aiRowEst[] array with default information - information
** to be used when we have not run the ANALYZE command.
**
** aiRowEst[0] is suppose to contain the number of elements in the index.
** Since we do not know, guess 1 million.  aiRowEst[1] is an estimate of the
** number of rows in the table that match any particular value of the
................................................................................
*/
void sqlite3DropIndex(Parse *pParse, SrcList *pName, int ifExists){
  Index *pIndex;
  Vdbe *v;
  sqlite3 *db = pParse->db;
  int iDb;

  if( NEVER(pParse->nErr>0) || db->mallocFailed ){
    goto exit_drop_index;
  }
  assert( pName->nSrc==1 );
  if( SQLITE_OK!=sqlite3ReadSchema(pParse) ){
    goto exit_drop_index;
  }
  pIndex = sqlite3FindIndex(db, pName->a[0].zName, pName->a[0].zDatabase);
................................................................................
**         sqlite3SrcListAppend(D,A,B,0);
**
** Then B is a table name and the database name is unspecified.  If called
** like this:
**
**         sqlite3SrcListAppend(D,A,B,C);
**
** Then C is the table name and B is the database name.  If C is defined
** then so is B.  In other words, we never have a case where:
**
**         sqlite3SrcListAppend(D,A,0,C);
*/
SrcList *sqlite3SrcListAppend(
  sqlite3 *db,        /* Connection to notify of malloc failures */
  SrcList *pList,     /* Append to this SrcList. NULL creates a new SrcList */
  Token *pTable,      /* Table to append */
  Token *pDatabase    /* Database of the table */
){
  struct SrcList_item *pItem;
  assert( pDatabase==0 || pTable!=0 );  /* Cannot have C without B */
  if( pList==0 ){
    pList = sqlite3DbMallocZero(db, sizeof(SrcList) );
    if( pList==0 ) return 0;
    pList->nAlloc = 1;
  }
  pList = sqlite3SrcListEnlarge(db, pList, 1, pList->nSrc);
  if( db->mallocFailed ){
................................................................................
    sqlite3SrcListDelete(db, pList);
    return 0;
  }
  pItem = &pList->a[pList->nSrc-1];
  if( pDatabase && pDatabase->z==0 ){
    pDatabase = 0;
  }
  if( pDatabase ){
    Token *pTemp = pDatabase;
    pDatabase = pTable;
    pTable = pTemp;
  }
  pItem->zName = sqlite3NameFromToken(db, pTable);
  pItem->zDatabase = sqlite3NameFromToken(db, pDatabase);
  return pList;
................................................................................
** Begin a transaction
*/
void sqlite3BeginTransaction(Parse *pParse, int type){
  sqlite3 *db;
  Vdbe *v;
  int i;

  assert( pParse!=0 );
  db = pParse->db;
  assert( db!=0 );
  if( db->aDb[0].pBt==0 ) return;
//  if( pParse->nErr || db->mallocFailed ) return;
  if( sqlite3AuthCheck(pParse, SQLITE_TRANSACTION, "BEGIN", 0, 0) ){
    return;
  }
  v = sqlite3GetVdbe(pParse);
  if( !v ) return;
  if( type!=TK_DEFERRED ){
    for(i=0; i<db->nDb; i++){
      sqlite3VdbeAddOp2(v, OP_Transaction, i, (type==TK_EXCLUSIVE)+1);
      sqlite3VdbeUsesBtree(v, i);
    }
................................................................................
/*
** Commit a transaction
*/
void sqlite3CommitTransaction(Parse *pParse){
  sqlite3 *db;
  Vdbe *v;

  assert( pParse!=0 );
  db = pParse->db;
  assert( db!=0 );
  if( db->aDb[0].pBt==0 ) return;
//  if( pParse->nErr || db->mallocFailed ) return;
  if( sqlite3AuthCheck(pParse, SQLITE_TRANSACTION, "COMMIT", 0, 0) ){
    return;
  }
  v = sqlite3GetVdbe(pParse);
  if( v ){
    sqlite3VdbeAddOp2(v, OP_AutoCommit, 1, 0);
  }
}

/*
** Rollback a transaction
*/
void sqlite3RollbackTransaction(Parse *pParse){
  sqlite3 *db;
  Vdbe *v;

  assert( pParse!=0 );
  db = pParse->db;
  assert( db!=0 );
  if( db->aDb[0].pBt==0 ) return;
//  if( pParse->nErr || db->mallocFailed ) return;
  if( sqlite3AuthCheck(pParse, SQLITE_TRANSACTION, "ROLLBACK", 0, 0) ){
    return;
  }
  v = sqlite3GetVdbe(pParse);
  if( v ){
    sqlite3VdbeAddOp2(v, OP_AutoCommit, 1, 1);
  }
}

/*
................................................................................

  /* Read the database schema. If an error occurs, leave an error message
  ** and code in pParse and return NULL. */
  if( SQLITE_OK!=sqlite3ReadSchema(pParse) ){
    return;
  }

  if( pName1==0 || NEVER(pName1->z==0) ){
    reindexDatabases(pParse, 0);
    return;
  }else if( NEVER(pName2==0) || pName2->z==0 ){
    char *zColl;
    assert( pName1->z );
    zColl = sqlite3NameFromToken(pParse->db, pName1);
    if( !zColl ) return;
    pColl = sqlite3FindCollSeq(db, ENC(db), zColl, 0);
    if( pColl ){

      reindexDatabases(pParse, zColl);
      sqlite3DbFree(db, zColl);

      return;
    }
    sqlite3DbFree(db, zColl);
  }
  iDb = sqlite3TwoPartName(pParse, pName1, pName2, &pObjName);
  if( iDb<0 ) return;
  z = sqlite3NameFromToken(db, pObjName);