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Overview
| Comment: | Do not flatten subqueries that contain an ORDER BY or GROUP BY clause and can be implemented using a co-routine. |
|---|---|
| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | descendants | both | prefer-coroutine-sort-subquery |
| Files: | files | file ages | folders |
| SHA3-256: |
042d655dd9002e8b89a798ad955b0285 |
| User & Date: | drh 2017-09-28 20:06:53 |
Context
|
2017-09-29
| ||
| 14:31 | Merge changes from trunk. (check-in: 06f432fb user: drh tags: prefer-coroutine-sort-subquery) | |
|
2017-09-28
| ||
| 20:06 | Do not flatten subqueries that contain an ORDER BY or GROUP BY clause and can be implemented using a co-routine. (check-in: 042d655d user: drh tags: prefer-coroutine-sort-subquery) | |
| 17:29 | Remove the (undocumented) query-planner control that prevents a "SELECT ALL" subquery in FROM clause from being implemented as a co-routine. This control was added by [a29e117d7ec], where it was called a "stop-gap". (check-in: ff2f5a31 user: drh tags: trunk) | |
Changes
Changes to src/select.c.
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/* Catch mismatch in the declared columns of a view and the number of
** columns in the SELECT on the RHS */
if( pTab->nCol!=pSub->pEList->nExpr ){
sqlite3ErrorMsg(pParse, "expected %d columns for '%s' but got %d",
pTab->nCol, pTab->zName, pSub->pEList->nExpr);
goto select_end;
}
isAggSub = (pSub->selFlags & SF_Aggregate)!=0;
if( flattenSubquery(pParse, p, i, isAgg, isAggSub) ){
/* This subquery can be absorbed into its parent. */
if( isAggSub ){
isAgg = 1;
p->selFlags |= SF_Aggregate;
|
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/* Catch mismatch in the declared columns of a view and the number of
** columns in the SELECT on the RHS */
if( pTab->nCol!=pSub->pEList->nExpr ){
sqlite3ErrorMsg(pParse, "expected %d columns for '%s' but got %d",
pTab->nCol, pTab->zName, pSub->pEList->nExpr);
goto select_end;
}
/* If the subquery contains an ORDER BY or GROUP BY clause and if
** it will be implemented as a co-routine, then do not flatten. This
** restriction allows SQL constructs like this:
**
** SELECT expensive_function(x)
** FROM (SELECT x FROM tab ORDER BY y LIMIT 10);
**
** The expensive_function() is only computed on the 10 rows that
** are output, rather than every row of the table.
*/
if( (pSub->pOrderBy!=0 || pSub->pGroupBy!=0)
&& i==0
&& (pTabList->nSrc==1
|| (pTabList->a[1].fg.jointype&(JT_LEFT|JT_CROSS))!=0)
&& OptimizationEnabled(db, SQLITE_SubqCoroutine)
){
continue;
}
isAggSub = (pSub->selFlags & SF_Aggregate)!=0;
if( flattenSubquery(pParse, p, i, isAgg, isAggSub) ){
/* This subquery can be absorbed into its parent. */
if( isAggSub ){
isAgg = 1;
p->selFlags |= SF_Aggregate;
|