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Message-ID: <20060606234031.168.qmail@web31807.mail.mud.yahoo.com>
Date: Tue, 6 Jun 2006 16:40:31 -0700 (PDT)
From: Richard Broersma Jr <rabroersma@yahoo.com>
Subject: Re: How To Exclude True Values
To: operationsengineer1@yahoo.com,
	"pgsql-sql@postgresql.org" <pgsql-sql@postgresql.org>
In-Reply-To: <20060606230141.3017.qmail@web33310.mail.mud.yahoo.com>
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> Richard, that is the result i would need given that
> data set.  i have to digest this version, though.
> 
> should this query be more efficient than the subquery
> version as the table starts to get large?

My experience is that Distinct On queries do not preform as well as their group by counter parts. 
I believe that others have also commented to the same effect.

To speed the query you could apply indexes on the group by fields and the join columns.

Also, I produced a second query using PostgreSQL:

select a.id_i, a.ir_id, a.test, a.stamp
from test a 

join
(
select max(stamp) as mstamp, id_i
from test
group by id_i
) b

on a.stamp = b.mstamp

where a.test = false
;

-- result

 id_i | ir_id | test |        stamp
------+-------+------+---------------------
    4 |     8 | f    | 2006-06-05 08:00:00