From: | Antonin Houska <ah(at)cybertec(dot)at> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Richard Guo <riguo(at)pivotal(dot)io>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Pulling up direct-correlated ANY_SUBLINK |
Date: | 2019-09-11 07:25:05 |
Message-ID: | 90438.1568186705@antos |
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Lists: | pgsql-hackers |
Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > Can we try to pull up direct-correlated ANY SubLink with the help of
> > LATERAL?
>
> Perhaps. But what's the argument that you'd end up with a better
> plan? LATERAL pretty much constrains things to use a nestloop,
> so I'm not sure there's anything fundamentally different.
I think that subquery pull-up is most beneficial when the queries (both the
subquery and the upper query) contain more than a few tables. In such a case,
if only a few tables reference the upper query (or if just a single one does),
the constraints imposed by LATERAL might be less significant.
Nevertheless, I don't know how to overcome the problems that I mentioned
upthread.
--
Antonin Houska
Web: https://www.cybertec-postgresql.com
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