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Get the "omit ORDER BY in FROM-clause subqueries" optimization working for the

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core test cases.

FossilOrigin-Name: e31c5888659ffd4c6d8b68627123df3bbb84bb010b7766b0a74877bf3ba1e52b
This commit is contained in:
drh
2021-07-16 01:19:19 +00:00
parent bb30123178
commit 0fb78f0cca
4 changed files with 20 additions and 14 deletions
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14
src/select.c
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@@ -6386,7 +6386,8 @@ int sqlite3Select(
/* If a FROM-clause subquery has an ORDER BY clause that is not
** really doing anything, then delete it now so that it does not
** interfere with query flattening.
** interfere with query flattening. See the discussion at
** https://sqlite.org/forum/forumpost/2d76f2bcf65d256a
**
** Beware of these cases where the ORDER BY clause may not be safely
** omitted:
@@ -6394,13 +6395,20 @@ int sqlite3Select(
** (1) There is also a LIMIT clause
** (2) The subquery was added to help with window-function
** processing
** (3) The outer query uses an aggregate function other than
** (3) The subquery is in the FROM clause of an UPDATE
** (4) The outer query uses an aggregate function other than
** the built-in count(), min(), or max().
** (5) The ORDER BY isn't going to accomplish anything because
** one of:
** (a) The outer query has a different ORDER BY clause
** (b) The subquery is part of a join
** See forum post 062d576715d277c8
*/
if( pSub->pOrderBy!=0
&& (p->pOrderBy!=0 || pTabList->nSrc>1) /* Condition (5) */
&& pSub->pLimit==0 /* Condition (1) */
&& (pSub->selFlags & SF_OrderByReqd)==0 /* Condition (2) */
&& (p->selFlags & SF_OrderByReqd)==0 /* Condition (3) */
&& (p->selFlags & SF_OrderByReqd)==0 /* Condition (3) and (4) */
&& OptimizationEnabled(db, SQLITE_OmitOrderBy)
){
SELECTTRACE(0x100,pParse,p,