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

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