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Turn restriction 20 on the query flattener into an assert since the situation

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restricted can no longer occur because of the more aggressive use of
co-routines.

FossilOrigin-Name: 4464f40ccd7c5553f4d44120ca6dac4e9445f08f083f7dcb3bd66b4413d818e0
This commit is contained in:
drh
2017-10-04 12:06:31 +00:00
parent 61b513e9e3
commit 7c58fea39f
3 changed files with 23 additions and 16 deletions
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23
src/select.c
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@@ -3382,11 +3382,12 @@ static void substSelect(
** (19) If the subquery uses LIMIT then the outer query may not
** have a WHERE clause.
**
** (20) If the sub-query is a compound select, then it must not use
** an ORDER BY clause. Ticket #3773. We could relax this constraint
** somewhat by saying that the terms of the ORDER BY clause must
** appear as unmodified result columns in the outer query. But we
** have other optimizations in mind to deal with that case.
** (**) Subsumed into (17d3). Was: If the sub-query is a compound select,
** then it must not use an ORDER BY clause - Ticket #3773. Because
** of (17d3), then only way to have a compound subquery is if it is
** the only term in the FROM clause of the outer query. But if the
** only term in the FROM clause has an ORDER BY, then it will be
** implemented as a co-routine and the flattener will never be called.
**
** (21) If the subquery uses LIMIT then the outer query may not be
** DISTINCT. (See ticket [752e1646fc]).
@@ -3520,9 +3521,6 @@ static int flattenSubquery(
** queries.
*/
if( pSub->pPrior ){
if( pSub->pOrderBy ){
return 0; /* Restriction (20) */
}
if( isAgg || (p->selFlags & SF_Distinct)!=0 || pSrc->nSrc!=1 ){
return 0; /* (17d1), (17d2), or (17d3) */
}
@@ -3557,6 +3555,15 @@ static int flattenSubquery(
*/
assert( (p->selFlags & SF_Recursive)==0 || pSub->pPrior==0 );
/* Ex-restriction (20):
** A compound subquery must be the only term in the FROM clause of the
** outer query by restriction (17d3). But if that term also has an
** ORDER BY clause, then the subquery will be implemented by co-routine
** and so the flattener will never be invoked. Hence, it is not possible
** for the subquery to be a compound and have an ORDER BY clause.
*/
assert( pSub->pPrior==0 || pSub->pOrderBy==0 );
/***** If we reach this point, flattening is permitted. *****/
SELECTTRACE(1,pParse,p,("flatten %s.%p from term %d\n",
pSub->zSelName, pSub, iFrom));