Select badges from table only if all requirements rows exist

Question

I got three tables. I want to query the badges table to get the badge if all the missions exists for the badge_id in the badge_requirements table.

In the case below, the badge would be returned because for badge_id = 1, all missions exist.

But if, for example, one record in the finished_missions table would not exist, then no badge would be returned.

The user_id will be supplied from the application.

table badges
+----+------+-------+
| id | name | image |
+----+------+-------+
| 1  | OHYE | path  |
+----+------+-------+
PK(id)

table badge_requirements
+------------+----------+
| mission_id | badge_id |
+------------+----------+
| 3          | 1        |
+------------+----------+
| 5          | 1        |
+------------+----------+
UNIQUE(mission_id, badge_id)
FK(mission_id, missions.id)
FK(badge_id, badges.id)

table finished_missions
+----+---------+------------+
| id | user_id | mission_id |
+----+---------+------------+
| 3  | 221     | 3          | // if any of these record doesn't exist
+----+---------+------------+
| 5  | 221     | 5          | // the badge associated with this mission would not be returned
+----+---------+------------+
PK(id)
FK(user_id, users.id)
FK(mission_id, missions.id)

EDIT Changed the missions table to finished_missions for better readability. The user id and mission id are just referencing the user and mission table.

EDIT 2 I've tried this, given from an answer:

SELECT * FROM badges b
INNER JOIN finished_missions fm ON (fm.user_id = 221)
INNER JOIN badge_requirements br ON (br.mission_id = fm.mission_id AND br.badge_id = b.id)

But it still returns the badge even if I have just one record in finished_missions table.

Answer 1

There are many ways. This should be one:

SELECT badge_id
FROM  (  -- count missions per badge for the given user
   SELECT br.badge_id, count(*) AS ct
   FROM   finished_missions fm
   JOIN   badge_requirements br USING (mission_id)
   WHERE  fm.user_id = 221
   GROUP  BY  1
   ) u  -- count missions per badge total
JOIN (
   SELECT br.badge_id, count(*) AS ct
   FROM   badge_requirements
   ) b USING (badge_id, ct)  -- only badges with the full count of missions

In addition to the constraints you declared there should also be a, UNIQUE(user, mission_id) on finished_missions to disallow duplicate entries. Or you have to use count(DISTINCT mission_id) AS ct in the first subquery, so you can rely on the count.

And UNIQUE(mission_id, badge_id) should really be the PK - or add a NOT NULL constraint for both columns.