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

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
query gives me what I want

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

count | item_id | price
-------+---------+-------
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 rows.
The result I'm looking for would look like this:

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?

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