From: Andreas Joseph Krogh <andreak@officenet.no>
Organization: OfficeNet AS
To: pgsql-sql@postgresql.org
Subject: Re: Returning array of IDs as a sub-query with group-by
Date: Sun, 26 Aug 2007 00:42:56 +0200
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On Saturday 25 August 2007 23:02:19 Ragnar wrote:
> On lau, 2007-08-25 at 17:55 +0200, Andreas Joseph Krogh wrote:
> > On Saturday 25 August 2007 17:10:57 Andreas Joseph Krogh wrote:
>
> [snip]
>
> > >  count | item_id | price | item_id_array
> > > -------+---------+-------+---------------
> > >      3 |       1 |   100 | {1,2,3}
> > >      6 |       1 |   200 | {4,5,6,7,8,9}
> > >      2 |       2 |   200 | {10,11}
> > >
> > > I tried this query which complains about an ungruoped column:
> > >
> > > SELECT COUNT(il.price), i.id AS item_id, il.price,
> > >  ARRAY(SELECT a.id FROM item_log a WHERE a.id =3D il.id) AS item_id_a=
rray
> > >   FROM item i, item_log il WHERE i.id =3D il.item_id GROUP BY il.pric=
e,
> > > i.id;
> > >
> > > ERROR:  subquery uses ungrouped column "il.id" from outer query
> > >
> > > Any hints?
> >
> > I found the following CREATE AGGREGATE suggestion in the PG-docs:
>
> [aggregate solution snipped]
>
> > If someone knows of a way without introducing a new AGGREGATE I'm still
> > interrested.
>
> you can allways do the ARRAY(SELECT...) outside the grouping:
> # select *,(select ARRAY(
>                          SELECT a.id
>                          FROM item_log as a
>                          WHERE foo.item_id=3Da.item_id
>                                AND foo.price=3Da.price
>                          )
>            ) AS item_id_array
> from (
>        select count(*),item_id, price
>        from item_log
>        group by item_id, price
>      ) as foo;
>
>  count | item_id | price | item_id_array
> -------+---------+-------+---------------
>      3 |       1 |   100 | {1,2,3}
>      6 |       1 |   200 | {4,5,6,7,8,9}
>      2 |       2 |   200 | {10,11}
> (3 rows)
>
>
> but i suspect the aggregate will perform better
>
> gnari

Ok, thanks.

=2D-=20
Andreas Joseph Krogh <andreak@officenet.no>
Senior Software Developer / Manager
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