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Where possible, transform the DISTINCT qualifier to a GROUP BY clause. GROUP BY clauses may be optimized by indices, DISTINCT qualifiers cannot. (CVS 4538)

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FossilOrigin-Name: e56331234791cf3d830a30e4cfa66682bdf2eed1
This commit is contained in:
danielk1977
2007-11-12 15:29:18 +00:00
parent 390025053e
commit 3c4809a201
6 changed files with 42 additions and 21 deletions
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17
src/select.c
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@@ -12,7 +12,7 @@
** This file contains C code routines that are called by the parser
** to handle SELECT statements in SQLite.
**
** $Id: select.c,v 1.359 2007/08/31 17:42:48 danielk1977 Exp $
** $Id: select.c,v 1.360 2007/11/12 15:29:19 danielk1977 Exp $
*/
#include "sqliteInt.h"
@@ -3067,6 +3067,15 @@ int sqlite3Select(
}
#endif
/* If possible, rewrite the query to use GROUP BY instead of
*/
if( p->isDistinct && !p->isAgg && !p->pGroupBy ){
p->pGroupBy = sqlite3ExprListDup(db, p->pEList);
pGroupBy = p->pGroupBy;
p->isDistinct = 0;
isDistinct = 0;
}
/* If there is an ORDER BY clause, then this sorting
** index might end up being unused if the data can be
** extracted in pre-sorted order. If that is the case, then the
@@ -3102,6 +3111,7 @@ int sqlite3Select(
*/
if( isDistinct ){
KeyInfo *pKeyInfo;
assert( isAgg || pGroupBy );
distinct = pParse->nTab++;
pKeyInfo = keyInfoFromExprList(pParse, p->pEList);
sqlite3VdbeOp3(v, OP_OpenEphemeral, distinct, 0,
@@ -3129,7 +3139,8 @@ int sqlite3Select(
/* Use the standard inner loop
*/
if( selectInnerLoop(pParse, p, pEList, 0, 0, pOrderBy, distinct, eDest,
assert(!isDistinct);
if( selectInnerLoop(pParse, p, pEList, 0, 0, pOrderBy, -1, eDest,
iParm, pWInfo->iContinue, pWInfo->iBreak, aff) ){
goto select_end;
}
@@ -3191,7 +3202,7 @@ int sqlite3Select(
if( db->mallocFailed ) goto select_end;
/* Processing for aggregates with GROUP BY is very different and
** much more complex tha aggregates without a GROUP BY.
** much more complex than aggregates without a GROUP BY.
*/
if( pGroupBy ){
KeyInfo *pKeyInfo; /* Keying information for the group by clause */