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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: Volker Grabsch <vog(at)notjusthosting(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Calculation of unused columns
Date: 2009-10-18 02:19:33
Message-ID: 28393.1255832373@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Sat, Oct 17, 2009 at 9:41 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> I've been thinking about this since your earlier mail, and I think it
>> would probably be possible to suppress unused columns in a non-flattened
>> subquery. I remain unconvinced that it's worth the trouble though.
>> A real (not handwavy) example would help make the case here.

> Are there any situations where this would enable join removal that
> otherwise wouldn't be possible?

Hmm, yeah maybe, now that we have some join removal logic.  Seems a bit
of a stretch to claim that's a common real-world case though.

			regards, tom lane

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