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Re: Subsorting GROUP BY data

From: tv(at)fuzzy(dot)cz
To: "Johnson, Michael L(dot)" <michael(dot)l(dot)johnson(at)ngc(dot)com>
Cc: pgsql-sql(at)postgresql(dot)org
Subject: Re: Subsorting GROUP BY data
Date: 2008-11-10 15:18:27
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-sql
What about replacing the table by

SELECT * FROM my_table ORDER BY num

i.e. something like

SELECT cat, LAST(id), LAST(num) FROM (SELECT * FROM my_table ORDER BY num)
AS foo GROUP_BY cat;

Hope it works, just guessing it might help :-)


> SELECT cat, MAX(num) FROM my_table GROUP_BY cat;
> But if I add the "id" column, of course it doesn't work, since it's not
> in an aggregate function or in the GROUP_BY clause.  So I found a post
> at
> which describes how to add a "FIRST" and "LAST" aggregate function to
> PGSQL.  However, first and last don't seem to help unless you are able
> to "subsort" the grouping by the # (ie, group by cat, then subsort on
> num, and select the "last" one of the group).
> I would think something like the following would work, except that PGSQL
> does not like the SQL generated (it basically says I can't have a
> GROUP_BY after an ORDER_BY).  And if I move the "ORDER_BY" to the end,
> that just orders the returned groupings, so that doesn't help me either.
> SELECT cat, LAST(id), LAST(num) FROM my_table ORDER_BY num GROUP_BY cat;
> So does anyone know how to sort *within* a grouping so that FIRST and
> LAST return meaningful results?

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Subject: Re: Subsorting GROUP BY data
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Subject: Subsorting GROUP BY data

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