Richard Guo <guofenglinux@gmail.com> writes:
> Hmm. I begin to wonder if it's better to use phinfo->ph_eval_at instead
> in build_joinrel_tlist when we check whether the PHV actually comes from
> the nullable side of an outer join.
I wondered about that too, but I think phrels is probably preferable,
because it is fundamentally a syntactic attribute and what we are
after here is matching the syntactic structure. I could be convinced
that that's wrong, but I'd want to see an actual counterexample.
> Even so it seems we still need to update phv->phrels in
> remove_rel_from_query when we remove a left join. Otherwise it'd be
> weird to observe that phrels contains some already-removed relids.
Agreed, that's a good catch. As the comment for remove_rel_from_query
says,
* We are not terribly thorough here.
It's not surprising that the requirements for it advance over time.
(At one point I wrote some code that taught it to clean out the
removed relids from EquivalenceClasses, which doesn't need
to happen right now because we don't ever put outer-join quals
into EquivalenceClasses. I don't think I included that in any
of the published versions of the patch series, but it's going to
need to reappear eventually.)
regards, tom lane
