Fix psql \d's query for identifying parent triggers.
The original coding (from
c33869cc3) failed with "more than one row
returned by a subquery used as an expression" if there were unrelated
triggers of the same tgname on parent partitioned tables. (That's
possible because statement-level triggers don't get inherited.) Fix
by applying LIMIT 1 after sorting the candidates by inheritance level.
Also, wrap the subquery in a CASE so that we don't have to execute it at
all when the trigger is visibly non-inherited. Aside from saving some
cycles, this avoids the need for a confusing and undocumented NULLIF().
While here, tweak the format of the emitted query to look a bit
nicer for "psql -E", and add some explanation of this subquery,
because it badly needs it.
Report and patch by Justin Pryzby (with some editing by me).
Back-patch to v13 where the faulty code came in.
Discussion: https://postgr.es/m/
20211217154356.GJ17618@telsasoft.com