Message-ID: <3DB6B7F7.2030609@klaster.net>
Date: Wed, 23 Oct 2002 16:53:43 +0200
From: Tomasz Myrta <jasiek@klaster.net>
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To: Stephan Szabo <sszabo@megazone23.bigpanda.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: sub-select with aggregate
References: <20021023071418.N4419-100000@megazone23.bigpanda.com>
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Uz.ytkownik Stephan Szabo napisa?:
> But you can't do that anyway, because you don't expose group_id
> in the original query.  I assume user_id was a mistake then and was
> meant to be group_id or that both were meant to be in the
> select list.
Yes, I meant group_id, but in orginal query I didn't have to add 
group_id to select list.

> In the first case changing the order means that the output
> group_id column is X.group_id rather than users.group_id
> (using removes one of them which is why group_id isn't
> ambiguous.  In the second it uses on to get both group_ids
> and exposes the one from X.
The problem isn't ambigous columns, but speed.
I think Postgres first performs sub-query with all records from table 
(it takes very long time). After this Postgres permforms joining table 
with sub-query. The question is: How to speed up query like this? How to 
give param group_id from first table (users) to subquery?
Tomasz Myrta