From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> |
Cc: | Peifeng Qiu <pgsql(at)qiupf(dot)dev>, "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, pgsql-hackers(at)lists(dot)postgresql(dot)org |
Subject: | Re: Optimize common expressions in projection evaluation |
Date: | 2022-12-05 04:47:53 |
Message-ID: | 3102800.1670215673@sss.pgh.pa.us |
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Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> po 5. 12. 2022 v 5:28 odesílatel Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> napsal:
>> I tend to agree with David that LATERAL offers a good-enough
>> solution in most cases ... but it is annoying that we accept
>> this syntax and then pessimize it.
> I agree, so there is a perfect solution like don't use .*, but on second
> hand any supported syntax should be optimized well or we should raise some
> warning about negative performance impact.
Yeah. I wonder if we could get the parser to automatically transform
SELECT (foo(t.x)).* FROM tab t
into
SELECT f.* FROM tab t, LATERAL foo(t.x) f
There are probably cases where this doesn't work or changes the
semantics subtly, but I suspect it could be made to work in
most cases of practical interest.
regards, tom lane
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