Re: BUG #19633: Unexpected results of IN (subquery) with a non-deterministic collation

On Thu, Sep 10, 2026 at 10:56 AM Andrey Rachitskiy <pl0h0yp1(at)gmail(dot)com> wrote:
> On backpatch the C change applies cleanly through 14. The regress
> SQL hunks also apply, but the EXPLAIN text is not identical across
> branches even when the counts are. I checked REL_19 through REL_14
> with --with-icu. After the fix the counts are 1/1/1 and 3 everywhere.
> The EXPLAIN differences are:
>
> - Unique Sort Key on REL_18 and older prints
> ((test2cs.x)::text) COLLATE case_insensitive
> where master/REL_19 print test2cs.x COLLATE case_insensitive
>
> - unique-index case on REL_17 through REL_14 comes out as
> Hash Semi Join rather than Hash Right Semi Join
>
> So the backpatch will need a small expected.

OK, I'll take care about this during backpatching.

I also like idea of usage of enable_sort all the version in this case.
This would simplify backpatching and reduce divergence between
versions.

I made two changes to the patch.

1) Dropped the two filler rows in test1cs. They were needed back when
that block used a private two-row table; test1cs already has four
rows. That's enough to get the desired plan.
2) Dropped "ALTER TABLE test2cs ALTER COLUMN x RESET (n_distinct)".
With no ANALYZE after it, it does not restore the statistics anyway,
and nothing later in the file reads test2cs.

I plan to push this and backpatch through 14, adjusting the expected
file per branch along the lines you described.

------
Regards,
Alexander Korotkov
Supabase