Re: [SQL] Join issue on a maximum value

[Heflin]

Bruno Wolff III wrote:

On Wed, Apr 21, 2004 at 14:29:34 -0400,
Heflin <[EMAIL PROTECTED]> 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.

Thanks!

I was actually trying to do it the more standard way, but I've been bungling up the syntax. I'm going to play with that some more, since it might be useful elsewhere.

The thing that disturbs me about your syntax is that I don't really see an assurance that I'll get the correct image_id. Any chance you can tell me why this works?

Thanks again,

-Heflin

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