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Avoid reevaluating WHERE and ORDER BY expressions that alias terms in the

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result set.  Ticket #3343.  Note that aliased GROUP BY expressions are still
evaluated twice. (CVS 5637)

FossilOrigin-Name: ab0292caa5887cc1bdc0e8c9d3f3502b83975440
This commit is contained in:
drh
2008-08-29 02:14:02 +00:00
parent 3fb120cb9d
commit 8b213899e8
8 changed files with 285 additions and 51 deletions
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92
src/resolve.c
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@ -14,12 +14,75 @@
** resolve all identifiers by associating them with a particular
** table and column.
**
** $Id: resolve.c,v 1.4 2008/08/25 17:23:29 drh Exp $
** $Id: resolve.c,v 1.5 2008/08/29 02:14:03 drh Exp $
*/
#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 */
const char *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 */
assert( iCol>=0 && iCol<pEList->nExpr );
pOrig = pEList->a[iCol].pExpr;
assert( pOrig!=0 );
assert( pOrig->flags & EP_Resolved );
db = pParse->db;
pDup = sqlite3ExprDup(db, pOrig);
if( pDup==0 ) return;
if( pDup->op!=TK_COLUMN && zType[0]!='G' ){
pDup = sqlite3PExpr(pParse, TK_AS, pDup, 0, 0);
if( pDup==0 ) return;
if( pEList->a[iCol].iAlias==0 ){
pEList->a[iCol].iAlias = ++pParse->nAlias;
}
pDup->iTable = pEList->a[iCol].iAlias;
}
if( pExpr->flags & EP_ExpCollate ){
pDup->pColl = pExpr->pColl;
pDup->flags |= EP_ExpCollate;
}
if( pExpr->span.dyn ) sqlite3DbFree(db, (char*)pExpr->span.z);
if( pExpr->token.dyn ) sqlite3DbFree(db, (char*)pExpr->token.z);
memcpy(pExpr, pDup, sizeof(*pExpr));
sqlite3DbFree(db, pDup);
}
/*
** Given the name of a column of the form X.Y.Z or Y.Z or just Z, look up
** that name in the set of source tables in pSrcList and make the pExpr
@ -218,7 +281,7 @@ static int lookupName(
for(j=0; j<pEList->nExpr; j++){
char *zAs = pEList->a[j].zName;
if( zAs!=0 && sqlite3StrICmp(zAs, zCol)==0 ){
Expr *pDup, *pOrig;
Expr *pOrig;
assert( pExpr->pLeft==0 && pExpr->pRight==0 );
assert( pExpr->pList==0 );
assert( pExpr->pSelect==0 );
@ -228,15 +291,7 @@ static int lookupName(
sqlite3DbFree(db, zCol);
return 2;
}
pDup = sqlite3ExprDup(db, pOrig);
if( pExpr->flags & EP_ExpCollate ){
pDup->pColl = pExpr->pColl;
pDup->flags |= EP_ExpCollate;
}
if( pExpr->span.dyn ) sqlite3DbFree(db, (char*)pExpr->span.z);
if( pExpr->token.dyn ) sqlite3DbFree(db, (char*)pExpr->token.z);
memcpy(pExpr, pDup, sizeof(*pExpr));
sqlite3DbFree(db, pDup);
resolveAlias(pParse, pEList, j, pExpr, "");
cnt = 1;
pMatch = 0;
assert( zTab==0 && zDb==0 );
@ -731,24 +786,11 @@ int sqlite3ResolveOrderGroupBy(
assert( pEList!=0 ); /* sqlite3SelectNew() guarantees this */
for(i=0, pItem=pOrderBy->a; i<pOrderBy->nExpr; i++, pItem++){
if( pItem->iCol ){
Expr *pE;
CollSeq *pColl;
int flags;
if( pItem->iCol>pEList->nExpr ){
resolveOutOfRangeError(pParse, zType, i+1, pEList->nExpr);
return 1;
}
pE = pItem->pExpr;
pColl = pE->pColl;
flags = pE->flags & EP_ExpCollate;
sqlite3ExprDelete(db, pE);
pE = sqlite3ExprDup(db, pEList->a[pItem->iCol-1].pExpr);
pItem->pExpr = pE;
if( pE && flags ){
pE->pColl = pColl;
pE->flags |= flags;
}
resolveAlias(pParse, pEList, pItem->iCol-1, pItem->pExpr, zType);
}
}
return 0;