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First pass at optimizing max()/min() as described in #2853. Some refinements to come. (CVS 4687)

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FossilOrigin-Name: c449e04f1870b1ff726c95c0bf1c6c6a22ca588a
This commit is contained in:
danielk1977
2008-01-05 17:39:29 +00:00
parent 5b6afba924
commit a9d1ccb9b0
11 changed files with 295 additions and 46 deletions
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57
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 1.386 2008/01/05 05:20:10 drh Exp $
** $Id: select.c,v 1.387 2008/01/05 17:39:30 danielk1977 Exp $
*/
#include "sqliteInt.h"
@@ -2625,6 +2625,33 @@ static int flattenSubquery(
}
#endif /* SQLITE_OMIT_VIEW */
/*
** Analyze the SELECT statement passed as an argument to see if it
** is a min() or max() query. Return ORDERBY_MIN or ORDERBY_MAX if
** it is, or 0 otherwise. At present, a query is considered to be
** a min()/max() query if:
**
** 1. The result set contains exactly one element, either
** min(x) or max(x), where x is a column identifier.
*/
static int minMaxQuery(Parse *pParse, Select *p){
Expr *pExpr;
ExprList *pEList = p->pEList;
if( pEList->nExpr!=1 ) return ORDERBY_NORMAL;
pExpr = pEList->a[0].pExpr;
pEList = pExpr->pList;
if( pExpr->op!=TK_AGG_FUNCTION || pEList==0 || pEList->nExpr!=1 ) return 0;
if( pEList->a[0].pExpr->op!=TK_AGG_COLUMN ) return ORDERBY_NORMAL;
if( pExpr->token.n!=3 ) return ORDERBY_NORMAL;
if( sqlite3StrNICmp((char*)pExpr->token.z,"min",3)==0 ){
return ORDERBY_MIN;
}else if( sqlite3StrNICmp((char*)pExpr->token.z,"max",3)==0 ){
return ORDERBY_MAX;
}
return ORDERBY_NORMAL;
}
/*
** Analyze the SELECT statement passed in as an argument to see if it
** is a simple min() or max() query. If it is and this query can be
@@ -2645,6 +2672,7 @@ static int flattenSubquery(
** The parameters to this routine are the same as for sqlite3Select().
** See the header comment on that routine for additional information.
*/
#if 0
static int simpleMinMaxQuery(Parse *pParse, Select *p, SelectDest *pDest){
Expr *pExpr;
int iCol;
@@ -2781,6 +2809,7 @@ static int simpleMinMaxQuery(Parse *pParse, Select *p, SelectDest *pDest){
return 1;
}
#endif
/*
** This routine resolves any names used in the result set of the
@@ -3268,10 +3297,12 @@ int sqlite3Select(
/* Check for the special case of a min() or max() function by itself
** in the result set.
*/
#if 0
if( simpleMinMaxQuery(pParse, p, pDest) ){
rc = 0;
goto select_end;
}
#endif
/* Check to see if this is a subquery that can be "flattened" into its parent.
** If flattening is a possiblity, do so and return immediately.
@@ -3345,7 +3376,7 @@ int sqlite3Select(
/* This case is for non-aggregate queries
** Begin the database scan
*/
pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, &pOrderBy);
pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, &pOrderBy, 0);
if( pWInfo==0 ) goto select_end;
/* If sorting index that was created by a prior OP_OpenEphemeral
@@ -3501,7 +3532,7 @@ int sqlite3Select(
*/
sqlite3VdbeResolveLabel(v, addrInitializeLoop);
sqlite3VdbeAddOp2(v, OP_Gosub, 0, addrReset);
pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, &pGroupBy);
pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, &pGroupBy, 0);
if( pWInfo==0 ) goto select_end;
if( pGroupBy==0 ){
/* The optimizer is able to deliver rows in group by order so
@@ -3606,14 +3637,30 @@ int sqlite3Select(
} /* endif pGroupBy */
else {
ExprList *pMinMax = 0;
u8 flag;
flag = minMaxQuery(pParse, p);
if( flag ){
pMinMax = sqlite3ExprListDup(db, p->pEList->a[0].pExpr->pList);
if( pMinMax ){
pMinMax->a[0].sortOrder = ((flag==ORDERBY_MIN)?0:1);
pMinMax->a[0].pExpr->op = TK_COLUMN;
}
}
/* This case runs if the aggregate has no GROUP BY clause. The
** processing is much simpler since there is only a single row
** of output.
*/
resetAccumulator(pParse, &sAggInfo);
pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, 0);
pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, &pMinMax, flag);
if( pWInfo==0 ) goto select_end;
updateAccumulator(pParse, &sAggInfo);
if( !pMinMax && flag ){
sqlite3VdbeAddOp2(v, OP_Goto, 0, pWInfo->iBreak);
VdbeComment((v, "%s() by index", (flag==ORDERBY_MIN?"min":"max")));
}
sqlite3WhereEnd(pWInfo);
finalizeAggFunctions(pParse, &sAggInfo);
pOrderBy = 0;
@@ -3622,6 +3669,8 @@ int sqlite3Select(
}
selectInnerLoop(pParse, p, p->pEList, 0, 0, 0, -1,
pDest, addrEnd, addrEnd, aff);
sqlite3ExprListDelete(pMinMax);
}
sqlite3VdbeResolveLabel(v, addrEnd);