Re: Teaching planner to short-circuit empty UNION/EXCEPT/INTERSECT inputs
| От | Mingli Zhang |
|---|---|
| Тема | Re: Teaching planner to short-circuit empty UNION/EXCEPT/INTERSECT inputs |
| Дата | |
| Msg-id | CANG7CAKhk+z0c7tO2LWXG6VtHrV3-uqc0zN=F=bjd=22uzmSrA@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Teaching planner to short-circuit empty UNION/EXCEPT/INTERSECT inputs (David Rowley <dgrowleyml@gmail.com>) |
| Ответы |
Re: Teaching planner to short-circuit empty UNION/EXCEPT/INTERSECT inputs
|
| Список | pgsql-hackers |
Hi,
David Rowley <dgrowleyml@gmail.com>于2025年10月2日 周四20:09写道：
On Thu, 2 Oct 2025 at 16:21, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> I'm wondering if it could be shortened a great deal by
> handling left-input-dummy and EXCEPT-ALL-with-right-input-dummy
> but leaving the EXCEPT-with-right-input-dummy case unimproved.
Good idea. Less code and still get to keep the one that did well in
the benchmark. See attached.
I ended up splitting the patch in two. 0001 for UNION only, then 0002
for the INTERSECT and EXCEPT.
David
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?
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