Some priority stuff

gistfile1.txt

mysql> select * from product; select * from category; select * from tag; select * from product_tag;
+----+----------+-------------+
| id | name     | category_id |
+----+----------+-------------+
|  1 | shampoo  |           1 |
|  2 | skocreme |           1 |
|  3 | vase     |           2 |
+----+----------+-------------+
3 rows in set (0.01 sec)

+----+----------+
| id | name     |
+----+----------+
|  1 | mad      |
|  2 | beverage |
+----+----------+
2 rows in set (0.00 sec)

+----+------+
| id | name |
+----+------+
|  1 | hund |
|  2 | kat  |
|  3 | and  |
+----+------+
3 rows in set (0.00 sec)

+----+------------+--------+
| id | product_id | tag_id |
+----+------------+--------+
|  1 |          1 |      1 |
|  2 |          1 |      2 |
|  3 |          1 |      3 |
|  4 |          2 |      3 |
|  5 |          2 |      2 |
+----+------------+--------+
5 rows in set (0.00 sec)

mysql> select pt.product_id, count(*) cnt from product_tag pt left join product p on pt.product_id=p.id group by pt.product_id order by cnt desc;
+------------+-----+
| product_id | cnt |
+------------+-----+
|          1 |   3 |
|          2 |   2 |
+------------+-----+
2 rows in set (0.01 sec)

mysql>