Teodor Sigaev <teodor@sigaev.ru> writes:
> SELECT
> *
> FROM
> t
> WHERE (
> CASE
> WHEN a%2 IN (SELECT c FROM tt) THEN a
> END IN (SELECT c FROM tt)
> );
> I suppose, the problem is connected to hashed subplan, but I'm not very familiar
> with executor. And this affects all supported versions of pgsql.
It seems to be a planner bug: it's doing the wrong thing with the
PARAM_SUBLINK Params for the nested IN SubLinks. (They don't look
to be nested textually, but they are, and convert_testexpr is
mistakenly replacing the inner one's Params when it should only
be replacing the outer one's Params.)
I think this has probably been broken since about 2005 :-(.
The comment on convert_testexpr claims it doesn't need to worry
about nested cases; which is true when it's called during
SS_process_sublinks, but not so much when it's called from
convert_ANY_sublink_to_join. Some digging in the git history
suggests that the latter call existed at the time, meaning the
comment was wrong even when written.
regards, tom lane