| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Richard Guo <guofenglinux(at)gmail(dot)com> |
| Cc: | Pg Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, "Finnerty, Jim" <jfinnert(at)amazon(dot)com> |
| Subject: | Re: Making Vars outer-join aware |
| Date: | 2022-07-13 14:09:23 |
| Message-ID: | 2217146.1657721363@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Richard Guo <guofenglinux(at)gmail(dot)com> writes:
> But I'm not sure which is better, to evaluate the expression below or
> above the outer join. It seems to me that if the size of base rel is
> large and somehow the size of the joinrel is small, evaluation above the
> outer join would win. And in the opposite case evaluation below the
> outer join would be better.
Reasonable question. But I think for the purposes of this patch,
it's better to keep the old behavior as much as we can. People
have probably relied on it while tuning queries. (I'm not saying
it has to be *exactly* bug-compatible, but simple cases like your
example probably should work the same.)
regards, tom lane
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