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Re: Calculation of unused columns

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Calculation of unused columns
Date: 2009-10-18 20:54:10
Message-ID: 10442.1255899250@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Sun, Oct 18, 2009 at 1:59 PM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
>> Even if country.id is a primary or unique key?

> Well, we currently don't have any logic for making inferences based on
> unique constraints.

Huh?
http://archives.postgresql.org/pgsql-committers/2009-09/msg00159.php

Admittedly it's just one case and there's lots more to be done, but it's
more than nothing.  So this is a *potential* argument for trying to trim
subquery outputs.  What I'm not sure about is whether there are common
cases where this would be applicable below a non-flattenable subquery.

			regards, tom lane

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