Message-ID: <447F2B19.1090608@oisinglynn.com>
Date: Thu, 01 Jun 2006 13:59:53 -0400
From: Oisin Glynn <me@oisinglynn.com>
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To: Collin Peters <cadiolis@gmail.com>
CC: pgsql-sql@postgresql.org
Subject: Re: Am I crazy or is this SQL not possible
References: <df01c91b0606011043g61328d6habaee8fa037a5ccf@mail.gmail.com>
In-Reply-To: <df01c91b0606011043g61328d6habaee8fa037a5ccf@mail.gmail.com>
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Collin Peters wrote:
> I am having some serious mental block here.  Here is the abstract
> version of my problem.  I have a table like this:
>
> unique_id (PK)   broadcast_id   date_sent      status
> 1                      1                     2005-04-04    30
> 2                      1                     2005-04-01     30
> 3                      1                     2005-05-20     10
> 4                      2                     2005-05-29     30
>
> So it is a table that stores broadcasts including the broadcast_id,
> the date sent, and the status of the broadcast.
>
> What I would like to do is simply get the last date_sent and it's
> status for every broadcast.  I can't do a GROUP BY because I can't put
> an aggregate on the status column.
>
> SELECT MAX(date_sent), status
> FROM broadcast_history
> GROUP BY broadcast_id
>
> How do I get the status for the most recent date_sent using GROUP BY?
>
> DISTINCT also doesn't work
>
> SELECT DISTINCT ON (email_broadcast_id) *
> FROM email_broadcast_history
> ORDER BY date_sent
>
> As you have to have the DISTINCT fields matching the ORDER BY fields.
> I have to ORDER BY date_sent, but I can't do a DISTINCT on date_sent
>
> I keep thinking am I missing something.  Does anybody have any ideas?
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: Don't 'kill -9' the postmaster

May not be the most efficient but seems to work here.

Select broadcast_id,status  from broadcast_history bh1 where 
bh1.date_sent = (select max(date_sent) from broadcast_history bh2 where 
bh1.broadcast_id=bh2.broadcast_id) order by bh1.broadcast_id;

Oisin