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Fix planner failure in some cases of sorting by an aggregate.

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An oversight introduced by the incremental-sort patches caused
"could not find pathkey item to sort" errors in some situations
where a sort key involves an aggregate or window function.

The basic problem here is that find_em_expr_usable_for_sorting_rel
isn't properly modeling what prepare_sort_from_pathkeys will do
later.  Rather than hoping we can keep those functions in sync,
let's refactor so that they actually share the code for
identifying a suitable sort expression.

With this refactoring, tlist.c's tlist_member_ignore_relabel
is unused.  I removed it in HEAD but left it in place in v13,
in case any extensions are using it.

Per report from Luc Vlaming.  Back-patch to v13 where the
problem arose.

James Coleman and Tom Lane

Discussion: https://postgr.es/m/91f3ec99-85a4-fa55-ea74-33f85a5c651f@swarm64.com
This commit is contained in:
Tom Lane
2021-04-20 11:32:02 -04:00
parent 95c3a1956e
commit 3753982441
7 changed files with 262 additions and 181 deletions
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28
src/backend/optimizer/util/tlist.c
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@@ -79,34 +79,6 @@ tlist_member(Expr *node, List *targetlist)
return NULL;
}
/*
* tlist_member_ignore_relabel
* Same as above, except that we ignore top-level RelabelType nodes
* while checking for a match. This is needed for some scenarios
* involving binary-compatible sort operations.
*/
TargetEntry *
tlist_member_ignore_relabel(Expr *node, List *targetlist)
{
ListCell *temp;
while (node && IsA(node, RelabelType))
node = ((RelabelType *) node)->arg;
foreach(temp, targetlist)
{
TargetEntry *tlentry = (TargetEntry *) lfirst(temp);
Expr *tlexpr = tlentry->expr;
while (tlexpr && IsA(tlexpr, RelabelType))
tlexpr = ((RelabelType *) tlexpr)->arg;
if (equal(node, tlexpr))
return tlentry;
}
return NULL;
}
/*
* tlist_member_match_var
* Same as above, except that we match the provided Var on the basis