| From: | Dennis Bjorklund <db(at)zigo(dot)dhs(dot)org> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Jack Coates <jack(at)lyris(dot)com>, pgsql-performance <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: query optimization question |
| Date: | 2004-01-30 07:19:43 |
| Message-ID: | Pine.LNX.4.44.0401300815390.30205-100000@zigo.dhs.org |
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| Lists: | pgsql-performance |
On Thu, 29 Jan 2004, Tom Lane wrote:
> > jackdb-# GROUP BY memberid_ HAVING (
>
> Um, that's not what I had in mind at all. Does GROUP BY actually do
> anything at all here? (You didn't answer me as to whether memberid_
> is a unique identifier or not, but if it is, this GROUP BY is just an
> expensive no-op.)
From your comment I assume that there is no transformation in pg that
detects that the group by columns are unique?
> this is all blue-sky speculation anyway. What I'm actually more
> interested in is your statement that MSSQL can do the original query
> quickly. I find that a bit hard to believe because I don't see any
> relevant optimization techniques.
Getting rid of the group by would not give that kind of speedup? Maybe
mssql manage to rewrite the query like that before executing.
--
/Dennis Björklund
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