Re: BUG #19804: "variable not found in subplan target list", DISTINCT agg over Gather`

Hi,

Tender Wang <tndrwang(at)gmail(dot)com> 于2026年10月30日周五 16:08写道：
>
> This has become a larger change than I expected, so I am sending it as
> WIP to get feedback.
>

Attached is v2.

The main change in this version fixes the compiler warnings reported
by CI for non-assert builds.
The variables nodenumsortkeys, nodeCollations, and nodeNullsFirst were
assigned only for use in Assert() calls, so they became unused when
assertions were compiled out.
I removed those assertion-only variables. create_append_plan() now
uses an explicit first_subplan flag when it needs information from the
first child.

I also adjusted the sort-column handling so that the common sortColIdx
chosen from the parent Append/MergeAppend targetlist is retained and
checked against every child, including the first one.
For MergeAppend, the first actual child still supplies the comparator
metadata the executor needs, but it no longer replaces the
parent-selected column layout.

The other changes are minor cleanup and formatting.

--
Thanks,
Tender Wang