| From: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
|---|---|
| To: | Dimitrios Apostolou <jimis(at)gmx(dot)net> |
| Cc: | pgsql-general(at)lists(dot)postgresql(dot)org |
| Subject: | Re: Inefficient query plan for SELECT ... EXCEPT ... |
| Date: | 2023-10-31 22:56:01 |
| Message-ID: | CAKFQuwYQUiqx5v96Xq6nAOf9sSwXntP8hwnPBjwiQbJjGiLPMA@mail.gmail.com |
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| Lists: | pgsql-general |
On Tue, Oct 31, 2023 at 3:41 PM Dimitrios Apostolou <jimis(at)gmx(dot)net> wrote:
>
> Is this worth a bug report? I can file one if the issue is not known.
> Or am I misunderstanding the implications of the SELECT-EXCEPT query?
>
> In the meantime I have replaced the query with a LEFT OUTER JOIN which
> performs much better,
I'd expect a NOT EXISTS query would also perform well and more accurately
reflect what you seem to be wanting here.
I could see maybe optimizing away the second independent query if the first
produces zero rows but it also doesn't seem like that productive an
optimization to attempt.
David J.
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