From: Andreas Joseph Krogh <andreak@officenet.no>
Organization: OfficeNet AS
To: pgsql-sql@postgresql.org
Subject: Returning array of IDs as a sub-query with group-by
Date: Sat, 25 Aug 2007 17:10:57 +0200
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Hi all.
I have the following schema:

create table item(
id serial primary key
);


create table item_log(
id serial primary key,
item_id integer not null references item(id),
price numeric NOT NULL
);


insert into item(id) values(1);
insert into item(id) values(2);
insert into item(id) values(3);
insert into item(id) values(4);

insert into item_log(item_id, price) values(1, 100);
insert into item_log(item_id, price) values(1, 100);
insert into item_log(item_id, price) values(1, 100);
insert into item_log(item_id, price) values(1, 200);
insert into item_log(item_id, price) values(1, 200);
insert into item_log(item_id, price) values(1, 200);
insert into item_log(item_id, price) values(1, 200);
insert into item_log(item_id, price) values(1, 200);
insert into item_log(item_id, price) values(1, 200);
insert into item_log(item_id, price) values(2, 200);
insert into item_log(item_id, price) values(2, 200);

Now, to get out all log-entries grouped on price with count the following=20
query gives me what I want

SELECT COUNT(il.price), i.id AS item_id, il.price FROM item i, item_log il=
=20
WHERE i.id =3D il.item_id GROUP BY il.price, i.id;

 count | item_id | price
=2D------+---------+-------
     3 |       1 |   100
     6 |       1 |   200
     2 |       2 |   200
(3 rows)

Now - I would like to return an ARRAY of item_log.id for each of the two ro=
ws.=20
The result I'm looking for would look like this:

 count | item_id | price | item_id_array
=2D------+---------+-------+---------------
     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_array
  FROM item i, item_log il WHERE i.id =3D il.item_id GROUP BY il.price, i.i=
d;

ERROR:  subquery uses ungrouped column "il.id" from outer query

Any hints?

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