/*
** 2008 August 18
**
** 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 routines used for walking the parser tree and
** resolve all identifiers by associating them with a particular
** table and column.
*************************************************************************
** Included in SQLite3 port to C#-SQLite; 2008 Noah B Hart
** C#-SQLite is an independent reimplementation of the SQLite software library
**
** SQLITE_SOURCE_ID: 2010-08-23 18:52:01 42537b60566f288167f1b5864a5435986838e3a3
**
*************************************************************************
*/
//#include "sqliteInt.h"
//#include <stdlib.h>
//#include <string.h>
/*
** Turn the pExpr expression into an alias for the iCol-th column of the
** result set in pEList.
**
** If the result set column is a simple column reference, then this routine
** makes an exact copy. But for any other kind of expression, this
** routine make a copy of the result set column as the argument to the
** TK_AS operator. The TK_AS operator causes the expression to be
** evaluated just once and then reused for each alias.
**
** The reason for suppressing the TK_AS term when the expression is a simple
** column reference is so that the column reference will be recognized as
** usable by indices within the WHERE clause processing logic.
**
** Hack: The TK_AS operator is inhibited if zType[0]=='G'. This means
** that in a GROUP BY clause, the expression is evaluated twice. Hence:
**
** SELECT random()%5 AS x, count(*) FROM tab GROUP BY x
**
** Is equivalent to:
**
** SELECT random()%5 AS x, count(*) FROM tab GROUP BY random()%5
**
** The result of random()%5 in the GROUP BY clause is probably different
** from the result in the result-set. We might fix this someday. Or
** then again, we might not...
*/
static void resolveAlias(
Parse pParse, /* Parsing context */
ExprList pEList, /* A result set */
int iCol, /* A column in the result set. 0..pEList.nExpr-1 */
Expr pExpr, /* Transform this into an alias to the result set */
string zType /* "GROUP" or "ORDER" or "" */
)
{
Expr pOrig; /* The iCol-th column of the result set */
Expr pDup; /* Copy of pOrig */
sqlite3 db; /* The database connection */
Debug.Assert( iCol >= 0 && iCol < pEList.nExpr );
pOrig = pEList.a[iCol].pExpr;
Debug.Assert( pOrig != null );
Debug.Assert( ( pOrig.flags & EP_Resolved ) != 0 );
db = pParse.db;
if ( pOrig.op != TK_COLUMN && ( zType.Length == 0 || zType[0] != 'G' ) )
{
pDup = sqlite3ExprDup( db, pOrig, 0 );
pDup = sqlite3PExpr( pParse, TK_AS, pDup, null, null );
if ( pDup == null )
return;
if ( pEList.a[iCol].iAlias == 0 )
{
pEList.a[iCol].iAlias = (u16)( ++pParse.nAlias );
}
pDup.iTable = pEList.a[iCol].iAlias;
}
else if ( ExprHasProperty( pOrig, EP_IntValue ) || pOrig.u.zToken == null )
{
pDup = sqlite3ExprDup( db, pOrig, 0 );
if ( pDup == null )
return;
}
else
{
string zToken = pOrig.u.zToken;
Debug.Assert( zToken != null );
pOrig.u.zToken = null;
pDup = sqlite3ExprDup( db, pOrig, 0 );
pOrig.u.zToken = zToken;
if ( pDup == null )
return;
Debug.Assert( ( pDup.flags & ( EP_Reduced | EP_TokenOnly ) ) == 0 );
pDup.flags2 |= EP2_MallocedToken;
pDup.u.zToken = zToken;// sqlite3DbStrDup( db, zToken );
}
if ( ( pExpr.flags & EP_ExpCollate ) != 0 )
{
pDup.pColl = pExpr.pColl;
pDup.flags |= EP_ExpCollate;
}
/* Before calling sqlite3ExprDelete(), set the EP_Static flag. This
** prevents ExprDelete() from deleting the Expr structure itself,
** allowing it to be repopulated by the memcpy() on the following line.
*/
ExprSetProperty( pExpr, EP_Static );
sqlite3ExprDelete( db, ref pExpr );
pExpr.CopyFrom( pDup ); //memcpy(pExpr, pDup, sizeof(*pExpr));
sqlite3DbFree( db, ref pDup );
}
