Re: SELECT TOP %d PERCENT, or SELECT ... LIMIT %d PERCENT ?

From: Grzegorz Jaskiewicz <gj(at)pointblue(dot)com(dot)pl>
To: "Hitoshi Harada" <umi(dot)tanuki(at)gmail(dot)com>
Cc: "Pg Hackers" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: SELECT TOP %d PERCENT, or SELECT ... LIMIT %d PERCENT ?
Date: 2008-10-12 13:07:14
Message-ID: B119A552-BB7C-4FE9-8EDE-7D4884BC603D@pointblue.com.pl
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that's a shame.
I figure, with the "WITH ... AS .." you can kind of speed up counts,
just by doing it once - now. But still, it would be great to be able
to use PERCENT, against estimate.
After all, imagine a table FOO with 5 rows, and something like this:

WITH c AS (select count(*)/4 as n from FOO) select * from FOO limit
(select n from c) offset (select n*X from c);

now X is for every 25%, but you wan't get to see last row if you use
offset 75 percent (X=3). Which kind of puts me off the idea of using
PERCENT anyway, because it isn't quite accurate.

So thanks for answer, I'll pass on this one. Hopefully there would be
another chance for me to write some patch in future.

ta.

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