From: Travis Whitton <tinymountain@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-sql@postgresql.org
Subject: Re: Grabbing Newest Records From Duplicates
Date: Fri, 16 Mar 2007 10:55:33 -0500
Message-ID: <cf9b4f3e0703160855q537eafe6yf3c3bbea090e5b6e@mail.gmail.com> (raw)
In-Reply-To: <7240.1174059340@sss.pgh.pa.us>
References: <cf9b4f3e0703160828s2cc0b9v6c01db6e8634e37e@mail.gmail.com>
<7240.1174059340@sss.pgh.pa.us>
One last question, using the "weather report" example, is it going to
improve performance for the DISTINCT ON query to add an index to the
location and time columns?
Thanks a lot,
Travis
On 3/16/07, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> "Travis Whitton" <tinymountain@gmail.com> writes:
> > Given the following test table, I want to grab only the newest record
> and
> > disregard any older duplicates based on name. Is this the most efficient
> way
> > to do it?
>
> No, it's gonna be pretty awful. The best way I know of involves
> DISTINCT ON (see the "weather reports" example in the SELECT reference
> page). Unfortunately that's a Postgres-only construct. If you want
> something portable then you'll need something messy with subqueries...
>
> regards, tom lane
>
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To: pgsql-sql@postgresql.org
Cc: tinymountain@gmail.com, tgl@sss.pgh.pa.us
Subject: Re: Grabbing Newest Records From Duplicates
In-Reply-To: <cf9b4f3e0703160855q537eafe6yf3c3bbea090e5b6e@mail.gmail.com>
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