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The query optimizer does a better job of optimizing out ORDER BY clauses

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that contain the rowid or which use indices that contain the rowid.
Ticket #2116. (CVS 3536)

FossilOrigin-Name: f245f5c2c2d337fe6458824beb7f9e721837765f
This commit is contained in:
drh
2006-12-20 03:24:19 +00:00
parent 2b7acc3551
commit cc19254de9
4 changed files with 197 additions and 29 deletions
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58
src/where.c
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@@ -16,7 +16,7 @@
** so is applicable. Because this module is responsible for selecting
** indices, you might also think of this module as the "query optimizer".
**
** $Id: where.c,v 1.233 2006/12/16 16:25:16 drh Exp $
** $Id: where.c,v 1.234 2006/12/20 03:24:19 drh Exp $
*/
#include "sqliteInt.h"
@@ -868,11 +868,19 @@ static int isSortingIndex(
/* Match terms of the ORDER BY clause against columns of
** the index.
**
** Note that indices have pIdx->nColumn regular columns plus
** one additional column containing the rowid. The rowid column
** of the index is also allowed to match against the ORDER BY
** clause.
*/
for(i=j=0, pTerm=pOrderBy->a; j<nTerm && i<pIdx->nColumn; i++){
for(i=j=0, pTerm=pOrderBy->a; j<nTerm && i<=pIdx->nColumn; i++){
Expr *pExpr; /* The expression of the ORDER BY pTerm */
CollSeq *pColl; /* The collating sequence of pExpr */
int termSortOrder; /* Sort order for this term */
int iColumn; /* The i-th column of the index. -1 for rowid */
int iSortOrder; /* 1 for DESC, 0 for ASC on the i-th index term */
const char *zColl; /* Name of the collating sequence for i-th index term */
pExpr = pTerm->pExpr;
if( pExpr->op!=TK_COLUMN || pExpr->iTable!=base ){
@@ -881,9 +889,22 @@ static int isSortingIndex(
return 0;
}
pColl = sqlite3ExprCollSeq(pParse, pExpr);
if( !pColl ) pColl = db->pDfltColl;
if( pExpr->iColumn!=pIdx->aiColumn[i] ||
sqlite3StrICmp(pColl->zName, pIdx->azColl[i]) ){
if( !pColl ){
pColl = db->pDfltColl;
}
if( i<pIdx->nColumn ){
iColumn = pIdx->aiColumn[i];
if( iColumn==pIdx->pTable->iPKey ){
iColumn = -1;
}
iSortOrder = pIdx->aSortOrder[i];
zColl = pIdx->azColl[i];
}else{
iColumn = -1;
iSortOrder = 0;
zColl = pColl->zName;
}
if( pExpr->iColumn!=iColumn || sqlite3StrICmp(pColl->zName, zColl) ){
/* Term j of the ORDER BY clause does not match column i of the index */
if( i<nEqCol ){
/* If an index column that is constrained by == fails to match an
@@ -899,8 +920,8 @@ static int isSortingIndex(
}
assert( pIdx->aSortOrder!=0 );
assert( pTerm->sortOrder==0 || pTerm->sortOrder==1 );
assert( pIdx->aSortOrder[i]==0 || pIdx->aSortOrder[i]==1 );
termSortOrder = pIdx->aSortOrder[i] ^ pTerm->sortOrder;
assert( iSortOrder==0 || iSortOrder==1 );
termSortOrder = iSortOrder ^ pTerm->sortOrder;
if( i>nEqCol ){
if( termSortOrder!=sortOrder ){
/* Indices can only be used if all ORDER BY terms past the
@@ -912,13 +933,25 @@ static int isSortingIndex(
}
j++;
pTerm++;
if( iColumn<0 ){
/* If the indexed column is the primary key and everything matches
** so far, then we are assured that the index can be used to sort
** because the primary key is unique and so none of the other columns
** will make any difference
*/
j = nTerm;
}
}
/* The index can be used for sorting if all terms of the ORDER BY clause
** are covered.
*/
*pbRev = sortOrder!=0;
if( j>=nTerm ){
*pbRev = sortOrder!=0;
/* All terms of the ORDER BY clause are covered by this index so
** this index can be used for sorting. */
return 1;
}
if( j==pIdx->nColumn && pIdx->onError!=OE_None ){
/* All terms of this index match some prefix of the ORDER BY clause
** and this index is UNIQUE, so this index can be used for sorting. */
return 1;
}
return 0;
@@ -939,8 +972,7 @@ static int sortableByRowid(
assert( pOrderBy!=0 );
assert( pOrderBy->nExpr>0 );
p = pOrderBy->a[0].pExpr;
if( pOrderBy->nExpr==1 && p->op==TK_COLUMN && p->iTable==base
&& p->iColumn==-1 ){
if( p->op==TK_COLUMN && p->iTable==base && p->iColumn==-1 ){
*pbRev = pOrderBy->a[0].sortOrder;
return 1;
}