From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Arjen van der Meijden <acmmailing(at)vulcanus(dot)its(dot)tudelft(dot)nl> |
Cc: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Large CASE-statement is pretty slow? |
Date: | 2004-03-14 21:09:40 |
Message-ID: | 25013.1079298580@sss.pgh.pa.us |
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Lists: | pgsql-performance |
Arjen van der Meijden <acmmailing(at)vulcanus(dot)its(dot)tudelft(dot)nl> writes:
> Anyway, I was looking into the usefullness of a INSERT INTO newtable
> SELECT field, field, CASE pkey WHEN x1 THEN y1 WHEN x2 THEN y2 etc END
> FROM oldtable
> The resulting select was about 1.7MB of query-text, mostly composed of
> the CASE-statement.
Hm, you mean one single SELECT, one single CASE? How many WHEN clauses
exactly? Exactly what did a typical clause of the CASE look like?
I wouldn't be too surprised to find some bit of code that's O(N^2) in
the number of arms of the CASE, or something like that; it's not an area
that we've ever felt the need to optimize. But I'd like a fairly
specific test case before trying to look into it.
regards, tom lane
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