mysql>   SELECT m.id, m.first_name, m.last_name, SUM(pl.quantity) AS kjop FROM purchases p
    ->   JOIN purchase_lines pl ON p.id = pl.purchase_id
    ->   JOIN products pr ON pl.product_id = pr.id
    ->   JOIN members m ON p.member_id = m.id
    ->   WHERE pr.category_id = 1
    ->   GROUP BY m.id
    ->   ORDER BY COUNT(m.id) DESC
    ->   LIMIT 5;
+----+------------+-----------+------+
| id | first_name | last_name | kjop |
+----+------------+-----------+------+
|  9 | Andreas    | Olsen     |    3 |
|  5 | Emilie     | Kielland  |    2 |
|  6 | Ida        | Hovind    |    1 |
|  2 | Tea        | Stene     |    1 |
| 10 | Kim        | L�g�en    |    1 |
+----+------------+-----------+------+
5 rows in set (0.00 sec)