| 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 |
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| 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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