| From: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> |
|---|---|
| To: | Kim Rose Carlsen <krc(at)hiper(dot)dk> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: Equivalence Classes when using IN |
| Date: | 2017-10-11 19:46:20 |
| Message-ID: | CAKJS1f-uCHFXOb6H6rVH+msh3+d4YyZFd5F1Ax7tzuFsXsrwyw@mail.gmail.com |
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| Lists: | pgsql-general |
On 12 October 2017 at 08:37, Kim Rose Carlsen <krc(at)hiper(dot)dk> wrote:
>
>> Yeah. The ORDER BY creates a partial optimization fence, preventing
>> any such plan from being considered.
>>>
>
> I can see in the general case it semanticly means different things If you allow the WHERE to pass through ORDER BY.
>
> A special case can be allowed for WHERE to pass the ORDER BY if the column is part of DISTINCT ON.
Yeah, we do allow predicates to be pushed down in that case.
--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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