| From: | David Rowley <dgrowleyml(at)gmail(dot)com> |
|---|---|
| To: | Mingli Zhang <zmlpostgres(at)gmail(dot)com> |
| Cc: | PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Subject: | Re: Teaching planner to short-circuit empty UNION/EXCEPT/INTERSECT inputs |
| Date: | 2025-10-02 22:24:45 |
| Message-ID: | CAApHDvoKNCo+7SJCggvx2Ca+ribq2W+S29naPqrMxbR5wPWZBQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, 3 Oct 2025 at 02:55, Mingli Zhang <zmlpostgres(at)gmail(dot)com> wrote:
> It seems that the optimization for `UNION ALL` is already implemented in the patch: it removes empty sub-paths and preserves the remaining ones.
> Should we add a test case to formally validate this behavior like Union cases?
If I were to do that, I'd have to come up with something that's
flatten_simple_union_all() proof. Maybe something like varying types
in the targetlist. I think it's probably not really worthwhile since
it's not testing any new code that is not already being tested by the
tests that I did add.
David
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