From: Robert Creager <Robert_Creager@LogicalChaos.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
To: PGSQL <pgsql-sql@postgresql.org>
To: PGSQL <pgsql-sql@postgresql.org>
Subject: Re: How can I get the last element out of GROUP BY sets?
Date: Mon, 19 Jan 2004 10:38:53 -0700
Message-ID: <20040119103853.01c87b83.Robert_Creager@LogicalChaos.org> (raw)
In-Reply-To: <20989.1074491070@sss.pgh.pa.us>
References: <20040118212834.7c667b9b.Robert_Creager@LogicalChaos.org>
<20989.1074491070@sss.pgh.pa.us>
When grilled further on (Mon, 19 Jan 2004 00:44:30 -0500),
Tom Lane <tgl@sss.pgh.pa.us> confessed:
> Robert Creager <Robert_Creager@LogicalChaos.org> writes:
> > ... one piece of data I need is the last value for each GROUP BY
> > period. Alas, I cannot figure out how to do this.
>
> SELECT DISTINCT ON (rather than GROUP BY) could get this done for you.
>
I had my whine all ready as to how I still couldn't figure it out, when I
figured it out:
...
SELECT p.period, etday
FROM (SELECT DISTINCT ON ( period )
date_trunc( 'hour', "when" ) AS period,
etday
FROM readings
ORDER BY period, "when" DESC) AS p
...
Thanks for the tip.
Cheers,
Rob
--
08:10:55 up 21 days, 21:58, 4 users, load average: 2.15, 2.06, 2.02
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To: pgsql-sql@postgresql.org
Cc: Robert_Creager@LogicalChaos.org, tgl@sss.pgh.pa.us
Subject: Re: How can I get the last element out of GROUP BY sets?
In-Reply-To: <20040119103853.01c87b83.Robert_Creager@LogicalChaos.org>
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