Re: BUG #17088: FailedAssertion in prepagg.c

On Thu, Jul 8, 2021 at 5:56 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:

Andrew Gierth <andrew@tao11.riddles.org.uk> writes:
> "Tom" == Tom Lane <tgl@sss.pgh.pa.us> writes:
>  Tom> Hmm. Maybe it'd be better if the default behavior in
>  Tom> expression_tree_walker/mutator did not include recursing into the
>  Tom> args, then?

> You'd think, but as I recall (I will re-check this to confirm) there
> were more places where we _did_ need to recurse (especially during parse
> analysis before we've matched up the sortgrouprefs), while most of the
> places where recursion needed to be explicitly avoided already needed
> special-case handling, so having the default the other way would likely
> have required a special-case almost everywhere.

Fair enough.  This is the kind of design choice that can be worth
revisiting later; but if the conclusion is still the same, fine with me.

I think the culprit is that when replacing correlation uplevel vars with
Params, we do not handle the SubLinks in the arguments of uplevel
GroupingFunc. We expect build_subplan should take care of it. But in
build_subplan, we ignore GroupingFunc incorrectly.

diff --git a/src/backend/optimizer/plan/subselect.c b/src/backend/optimizer/plan/subselect.c
index 0881a208ac..e4918f275e 100644
--- a/src/backend/optimizer/plan/subselect.c
+++ b/src/backend/optimizer/plan/subselect.c
@@ -364,7 +364,8 @@ build_subplan(PlannerInfo *root, Plan *plan, PlannerInfo *subroot,
                 * SS_replace_correlation_vars).  Do that now.
                 */
                if (IsA(arg, PlaceHolderVar) ||
-                       IsA(arg, Aggref))
+                       IsA(arg, Aggref) ||
+                       IsA(arg, GroupingFunc))
                        arg = SS_process_sublinks(root, arg, false);