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