Postgres group by - sql

Question

When I run a query, these are the results presented to me:
id account_id score active item_id
5 78 9 true 4
6 78 1 true 4
7 78 9 true 6
8 78 5 true 7
9 78 5 true 8
10 78 5 true 8
I'd like the output to look like this by combining item_id's based on score:
id account_id score active item_id
* 78 10 true 4
7 78 9 true 6
8 78 5 true 7
* 78 10 true 8
My query that returns that info looks like this:
SELECT item.id, item.account_id, itemaudit.score, itemrevision.active, itemaudit.item_id
from item
left join itemrevision on item.id = itemrevision.id
join itemaudit on item.id = itemaudit.id
where itemrevision.active = true
;
The bit I'm missing is when 'item_id' is not distinct, combine/sum the value of 'score'. I'm not sure how to do this step.
The schema looks like this:
CREATE TABLE item
(id integer, account_id integer);
CREATE TABLE itemaudit
(id integer, item_id integer, score integer);
CREATE TABLE itemrevision
(id int, active boolean, item_id int);
INSERT INTO item
(id, account_id)
VALUES
(5, 78),
(6, 78),
(7, 78),
(8, 78),
(9, 78),
(10, 78)
;
INSERT INTO itemaudit
(id, item_id, score)
VALUES
(5, 4, 5),
(6, 4, 1),
(7, 6, 9),
(8, 7, 10),
(9, 8, 1),
(10, 8, 9)
;
INSERT INTO itemrevision
(id, active, item_id)
VALUES
(5, true, 4),
(6, true, 4),
(7, true, 6),
(8, true, 7),
(9, true, 7),
(10, true, 8)
;

Answer 1

If I understand correctly, you just want an aggregation query:
select ia.item_id, sum(ia.score) as score
from item i join -- the `where` clause turns this into an inner join
itemrevision ir
on i.id = ir.id join
itemaudit ia
on i.id = ia.id
where ir.active = true
group by ia.item_id;
Notes:
I changed the left join to an inner join, because the where clause has this effect anyway.
Table aliases make the query easier to write and to read.
In an aggregation query, the other columns are not appropriate.

Answer 2

I think you want something like this..
SELECT
CASE
WHEN array_length(array_agg(id),1) = 1
THEN (array_agg(id))[1]::text
ELSE '*'
END AS id,
account_id,
sum(score) AS score,
item_id
FROM item
GROUP BY account_id, item_id
ORDER BY account_id, item_id;
id | account_id | score | item_id
----+------------+-------+---------
* | 78 | 10 | 4
7 | 78 | 9 | 6
8 | 78 | 5 | 7
* | 78 | 10 | 8
(4 rows)
While this is what you want the simpler versions is more detailed and better.
SELECT
array_agg(id) AS id,
account_id,
sum(score) AS score,
item_id
FROM item
GROUP BY account_id, item_id
ORDER BY account_id, item_id;
id | account_id | score | item_id
--------+------------+-------+---------
{5,6} | 78 | 10 | 4
{7} | 78 | 9 | 6
{8} | 78 | 5 | 7
{9,10} | 78 | 10 | 8
(4 rows)