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Re: DISTINCT -> GROUP BY

From: "Pavel Stehule" <pavel(dot)stehule(at)gmail(dot)com>
To: "David Fetter" <david(at)fetter(dot)org>
Cc: "PG Hackers" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: DISTINCT -> GROUP BY
Date: 2008-06-03 14:10:35
Message-ID: 162867790806030710k1de1dc9ey3fafcc65d3515dbe@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
2008/6/3 David Fetter <david(at)fetter(dot)org>:
> On Tue, Jun 03, 2008 at 03:36:44PM +0200, Pavel Stehule wrote:
>> Hello David
>>
>> http://www.postgresql.org/docs/faqs.TODO.html
>>
>> Consider using hash buckets to do DISTINCT, rather than sorting This
>> would be beneficial when there are few distinct values. This is
>> already used by GROUP BY.
>
> It's nice to see that this is kinda on the TODO, but it doesn't
> address the question I asked, which is, "how would I get the planner
> to rewrite DISTINCTs as the equivalent GROUP BYs?" :)

you can't to do it :(

Pavel

>
> Any hints?
>
> Cheers,
> David.
> --
> David Fetter <david(at)fetter(dot)org> http://fetter.org/
> Phone: +1 415 235 3778  AIM: dfetter666  Yahoo!: dfetter
> Skype: davidfetter      XMPP: david(dot)fetter(at)gmail(dot)com
>
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