From: | Filip Rembiałkowski <filip(dot)rembialkowski(at)gmail(dot)com> |
---|---|
To: | Bill Reynolds <Bill(dot)Reynolds(at)ateb(dot)com> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Group by and lmit |
Date: | 2010-11-04 00:07:00 |
Message-ID: | AANLkTikz7yGrQ5e-zo-fGqhWn_B4OG5Lc0aWPpHrmTeC@mail.gmail.com |
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Lists: | pgsql-general |
2010/11/2 Bill Reynolds <Bill(dot)Reynolds(at)ateb(dot)com>:
> I’m using postgres 8.3.7.
that's a pity because in 8.4 we have window functions which make this
possible in one query:
select * from (
select x, y, count(*) as counter,
row_number() over(partition by x order by count(*)) rn
from mytable
group by x, y order by x, count(*), y
) subq where subq.rn <= 5;
in 8,3 you will have to use some tricks... for example, temporary
sequence for every group.
CREATE LANGUAGE plpgsql;
create or replace function exec(text) returns text as 'begin execute
$1;return $1;end' language plpgsql;
select exec('create temp sequence tmpseq'||x) from (select distinct x
from mytable) q;
select x,y,counter from (select x, y, count(*) as counter from mytable
group by x, y order by x, counter, y) subq where
nextval(quote_ident('tmpseq'||x))<=5;
--
Filip Rembiałkowski
JID,mailto:filip(dot)rembialkowski(at)gmail(dot)com
http://filip.rembialkowski.net/
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