| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | David Rowley <dgrowleyml(at)gmail(dot)com> |
| Cc: | Jeevan Chalke <jeevan(dot)chalke(at)enterprisedb(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Marti Raudsepp <marti(at)juffo(dot)org>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Allowing NOT IN to use ANTI joins |
| Date: | 2014-07-11 01:11:18 |
| Message-ID: | 15174.1405041078@sss.pgh.pa.us |
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| Thread: | |
| Lists: | pgsql-hackers |
I wrote:
> We could no doubt fix this by also insisting that the left-side vars
> be provably not null, but that's going to make the patch even slower
> and even less often applicable. I'm feeling discouraged about whether
> this is worth doing in this form.
Hm ... actually, there might be a better answer: what about transforming
WHERE (x,y) NOT IN (SELECT provably-not-null-values FROM ...)
to
WHERE <antijoin condition> AND x IS NOT NULL AND y IS NOT NULL
?
Of course this would require x/y not being volatile, but if they are,
we're not going to get far with optimizing the query anyhow.
regards, tom lane
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