From: hubert depesz lubaczewski <depesz@depesz.com>
To: Gregory Stark <stark@enterprisedb.com>
Cc: JS Ubei <jsubei@yahoo.fr>
Cc: pgsql-performance@postgresql.org
Subject: Re: optimize query with a maximum(date) extraction
Date: Wed, 5 Sep 2007 15:22:50 +0200
Message-ID: <20070905132250.GA30304@depesz.com> (raw)
In-Reply-To: <87abs1qrhu.fsf@oxford.xeocode.com>
References: <302443.65402.qm@web26209.mail.ukl.yahoo.com>
<87abs1qrhu.fsf@oxford.xeocode.com>
On Wed, Sep 05, 2007 at 12:30:21PM +0100, Gregory Stark wrote:
> SELECT DISTINCT ON (id) id, the_date AS min_date FROM my_table ORDER BY id, the_date ASC
> SELECT DISTINCT ON (id) id, the_date AS max_date FROM my_table ORDER BY id, the_date DESC
> I think the first of these can actually use your index but the latter can't
> unless you create one for it specifically (which is not so easy -- it'll be
> easier in 8.3 though). Worse, I'm not really sure it'll be any faster than the
> query you already have.
it's easy to fix the second query (fix to use index) - just change order
by to:
order by id desc, the_date desc.
depesz
--
quicksil1er: "postgres is excellent, but like any DB it requires a
highly paid DBA. here's my CV!" :)
http://www.depesz.com/ - blog dla ciebie (i moje CV)
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To: pgsql-performance@postgresql.org
Cc: depesz@depesz.com, stark@enterprisedb.com, jsubei@yahoo.fr
Subject: Re: optimize query with a maximum(date) extraction
In-Reply-To: <20070905132250.GA30304@depesz.com>
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