Re: Returning array of IDs as a sub-query with group-by

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 = il.id) AS item_id_array
> > > FROM item i, item_log il WHERE i.id = il.item_id GROUP BY il.price,
> > > 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=a.item_id
> AND foo.price=a.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.

--
Andreas Joseph Krogh <andreak(at)officenet(dot)no>
Senior Software Developer / Manager
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