Re: simple? join

From: "Christopher Kings-Lynne" <chriskl(at)familyhealth(dot)com(dot)au>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "Frank Bax" <fbax(at)sympatico(dot)ca>
Cc: <pgsql-sql(at)postgresql(dot)org>
Subject: Re: simple? join
Date: 2002-01-08 01:54:29
Message-ID: GNELIHDDFBOCMGBFGEFOCEAMCBAA.chriskl@familyhealth.com.au
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> So, when and if we get around to implementing this particular SQL99
> feature, what you are suggesting will work. Right now it doesn't
> (and I'll wager that darn few other SQL implementations support this
> feature as yet, either).

I think MySQL does. I always found it strange that I had to add columns to
the group by clause in postgres that were functionally dependent on the
"real" grouped variable.

In fact, before I realised that you had to add them to the group by clause,
I just wrapped the functionally dependent fields in a MAX function (or min,
whatever).

ie. SELECT orders.product_id, MAX(product_name), MAX(unit_price) FROM
products NATURAL JOIN orders GROUP BY orders.product_id;

In fact, if one created a 'do nothing' aggregate function, you could avoid
having to add things to the group by clause in a cleaner fashion.

Chris

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