From: Andreas Joseph Krogh <andreak@officenet.no>
To: pgsql-sql@postgresql.org
Subject: Re: Returning array of IDs as a sub-query with group-by
Date: Sat, 25 Aug 2007 17:55:30 +0200
Message-ID: <200708251755.30291.andreak@officenet.no> (raw)
In-Reply-To: <200708251710.57557.andreak@officenet.no>
References: <200708251710.57557.andreak@officenet.no>
On Saturday 25 August 2007 17:10:57 Andreas Joseph Krogh wrote:
> 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?
I found the following CREATE AGGREGATE suggestion in the PG-docs:
CREATE AGGREGATE array_accum (anyelement)
(
sfunc = array_append,
stype = anyarray,
initcond = '{}'
);
With this I can easily issue:
SELECT COUNT(il.price), i.id AS item_id, il.price,
array_accum(il.id) AS item_id_array
FROM item i, item_log il WHERE i.id = il.item_id GROUP BY il.price, i.id;
Which does what I want:
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)
If someone knows of a way without introducing a new AGGREGATE I'm still
interrested.
--
Andreas Joseph Krogh <andreak@officenet.no>
Senior Software Developer / Manager
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Subject: Re: Returning array of IDs as a sub-query with group-by
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