Date: Wed, 21 Apr 2004 13:51:22 -0500
From: Bruno Wolff III <bruno@wolff.to>
To: Heflin <hhogan@tampabay.rr.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: Join issue on a maximum value
Message-ID: <20040421185122.GA31195@wolff.to>
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	pgsql-sql@postgresql.org
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On Wed, Apr 21, 2004 at 14:29:34 -0400,
  Heflin <hhogan@tampabay.rr.com> wrote:
> 
> So a basic JOIN gets this:
> 
> SELECT auction.auction_id, image.image_id, image.image_descr
> FROM auction JOIN image ON auction.auction_id = image.auction_id
> WHERE auction.auction_owner = 'Mabel';
> 
> Now the problem: I can't seem to remember how to get only the max value 
> for the image_id for each auction_id so that the result set would be:

The postgres specific way of doing this is:
SELECT DISTINCT ON (auction.auction_id)
    auction.auction_id, image.image_id, image.image_descr
  FROM auction JOIN image ON auction.auction_id = image.auction_id
  WHERE auction.auction_owner = 'Mabel'
  ORDER BY auction.auction_id, image.image_id DESC
;

The more standard way to do it would be joining auction and image
with a group by and max to get the highest image_id and then joining
that result to image again to get the corresponding description.