database/sqlite
1
0
Fork 0
mirror of https://github.com/sqlite/sqlite.git synced 2025-11-12 13:01:09 +03:00
Code Activity

Attempt to further generalize the min/max optimization so that, if an appropriate index exists, it can be used by any aggregate query that contains only a single aggregate of the form max(colname) or min(colname) and does not contain a GROUP BY clause.

Browse Source 
FossilOrigin-Name: 7280e14cd8f55896451847b432171e8750a07c81
This commit is contained in:
dan
2012-12-13 16:37:10 +00:00
parent 32055c2499
commit 4ac391fc05
4 changed files with 144 additions and 36 deletions
Download Patch File Download Diff File Expand all files Collapse all files

69
src/select.c
View File

@@ -3160,34 +3160,43 @@ static int flattenSubquery(
#endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */
/*
** Analyze the SELECT statement passed as an argument to see if it
** is a min() or max() query. Return WHERE_ORDERBY_MIN or WHERE_ORDERBY_MAX if
** it is, or 0 otherwise. At present, a query is considered to be
** a min()/max() query if:
** Based on the contents of the AggInfo structure indicated by the first
** argument, this function checks if the following are true:
**
** 1. There is a single object in the FROM clause.
** * the query contains just a single aggregate function,
** * the aggregate function is either min() or max(), and
** * the argument to the aggregate function is a column value.
**
** 2. There is a single expression in the result set, and it is
** either min(x) or max(x), where x is a column reference.
** If all of the above are true, then WHERE_ORDERBY_MIN or WHERE_ORDERBY_MAX
** is returned as appropriate. Also, *ppMinMax is set to point to the
** list of arguments passed to the aggregate before returning.
**
** Or, if the conditions above are not met, *ppMinMax is set to 0 and
** WHERE_ORDERBY_NORMAL is returned.
*/
static u8 minMaxQuery(Select *p){
Expr *pExpr;
ExprList *pEList = p->pEList;
static u8 minMaxQuery(AggInfo *pAggInfo, ExprList **ppMinMax){
int eRet = WHERE_ORDERBY_NORMAL; /* Return value */
if( pEList->nExpr!=1 ) return WHERE_ORDERBY_NORMAL;
pExpr = pEList->a[0].pExpr;
if( pExpr->op!=TK_AGG_FUNCTION ) return 0;
if( NEVER(ExprHasProperty(pExpr, EP_xIsSelect)) ) return 0;
pEList = pExpr->x.pList;
if( pEList==0 || pEList->nExpr!=1 ) return 0;
if( pEList->a[0].pExpr->op!=TK_AGG_COLUMN ) return WHERE_ORDERBY_NORMAL;
assert( !ExprHasProperty(pExpr, EP_IntValue) );
if( sqlite3StrICmp(pExpr->u.zToken,"min")==0 ){
return WHERE_ORDERBY_MIN;
}else if( sqlite3StrICmp(pExpr->u.zToken,"max")==0 ){
return WHERE_ORDERBY_MAX;
*ppMinMax = 0;
if( pAggInfo->nFunc==1 ){
Expr *pExpr = pAggInfo->aFunc[0].pExpr; /* Aggregate function */
ExprList *pEList = pExpr->x.pList; /* Arguments to agg function */
assert( pExpr->op==TK_AGG_FUNCTION );
if( pEList && pEList->nExpr==1 && pEList->a[0].pExpr->op==TK_AGG_COLUMN ){
const char *zFunc = pExpr->u.zToken;
if( sqlite3StrICmp(zFunc, "min")==0 ){
eRet = WHERE_ORDERBY_MIN;
*ppMinMax = pEList;
}else if( sqlite3StrICmp(zFunc, "max")==0 ){
eRet = WHERE_ORDERBY_MAX;
*ppMinMax = pEList;
}
}
}
return WHERE_ORDERBY_NORMAL;
assert( *ppMinMax==0 || (*ppMinMax)->nExpr==1 );
return eRet;
}
/*
@@ -4527,11 +4536,17 @@ int sqlite3Select(
** Refer to code and comments in where.c for details.
*/
ExprList *pMinMax = 0;
u8 flag = minMaxQuery(p);
u8 flag = WHERE_ORDERBY_NORMAL;
assert( p->pGroupBy==0 );
assert( flag==0 );
if( p->pHaving==0 ){
flag = minMaxQuery(&sAggInfo, &pMinMax);
}
assert( flag==0 || (pMinMax!=0 && pMinMax->nExpr==1) );
if( flag ){
assert( !ExprHasProperty(p->pEList->a[0].pExpr, EP_xIsSelect) );
assert( p->pEList->a[0].pExpr->x.pList->nExpr==1 );
pMinMax = sqlite3ExprListDup(db, p->pEList->a[0].pExpr->x.pList,0);
pMinMax = sqlite3ExprListDup(db, pMinMax, 0);
pDel = pMinMax;
if( pMinMax && !db->mallocFailed ){
pMinMax->a[0].sortOrder = flag!=WHERE_ORDERBY_MIN ?1:0;