Many hyperlinks are disabled.
Use anonymous login
to enable hyperlinks.
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 |
| Timelines: | family | ancestors | descendants | both | prefer-coroutine-sort-subquery |
| Files: | files | file ages | folders |
| SHA3-256: |
042d655dd9002e8b89a798ad955b0285 |
| User & Date: | drh 2017-09-28 20:06:53.014 |
Context
|
2017-09-29
| ||
| 14:31 | Merge changes from trunk. (check-in: 06f432fb7c 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: 042d655dd9 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: ff2f5a31a2 user: drh tags: trunk) | |
Changes
Changes to src/select.c.
| ︙ | ︙ | |||
5200 5201 5202 5203 5204 5205 5206 5207 5208 5209 5210 5211 5212 5213 |
/* 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;
| > > > > > > > > > > > > > > > > > > > | 5200 5201 5202 5203 5204 5205 5206 5207 5208 5209 5210 5211 5212 5213 5214 5215 5216 5217 5218 5219 5220 5221 5222 5223 5224 5225 5226 5227 5228 5229 5230 5231 5232 |
/* 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;
|
| ︙ | ︙ |