From: | Peter Eisentraut <peter_e(at)gmx(dot)net> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | pgsql-hackers(at)postgresql(dot)org, pgsql-sql(at)postgresql(dot)org |
Subject: | Re: [HACKERS] DISTINCT ON: speak now or forever hold your peace |
Date: | 2000-01-26 18:34:54 |
Message-ID: | Pine.LNX.4.21.0001260143120.9535-100000@localhost.localdomain |
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Lists: | pgsql-hackers pgsql-sql |
On 2000-01-24, Tom Lane mentioned:
> If I don't hear loud hollers very soon, I'm going to eliminate the
> DISTINCT ON "feature" for 7.0. As previously discussed, this feature
> is not standard SQL and has no clear semantic interpretation.
Our documents say that DISTINCT ON is equivalent to GROUP BY. I still
don't see why that wouldn't be true. You can always rewrite
select distinct on a a,b from test
as
select a, xxx(b) from test group by a
where xxx is some aggregate function (presumably min or max).
You can also rewrite
select distinct on a a,b,c from test
as
select a, b, c from test group by a, b, c
or using some aggregates here as well. At least you can control your
results that way.
--
Peter Eisentraut Sernanders väg 10:115
peter_e(at)gmx(dot)net 75262 Uppsala
http://yi.org/peter-e/ Sweden
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