MySQL query table filtering issue - mysql

Question

I've been struggling on the following.
I have 3 tables: players, players_clothes, and teams_clothes.
Table players:
id user team_id
1 tom 4
2 robo 5
3 bob 4
So tom and bob are both on the same team
Table players_clothes:
id clothes_id p_id
1 13 1
2 35 3
3 45 3
Bob has clothing article 35 and 45, robo has none.
Table teams_clothes:
id clothes_id team_id
1 35 4
2 45 4
3 55 4
4 65 5
This shows which teams have rights to which articles of clothing. The problem: tom is wearing an article of clothing that does no belong to his team... Let's assume this is illegal.
I'm having trouble figuring out how to capture all those who are wearing illegal clothes for a particular team.
SELECT pc.clothes_id FROM players AS p
JOIN players_clothes AS pc
ON p.id = pc.p_id
AND p.team_id = 4 GROUP BY pc.clothes_id
(I group by players_clothes.clothes_id because believe it or not, two players can be assigned the same piece of clothing)
I think this results the following set (13, 35, 45)
Now I would like to check against the actual set of clothes that team 4 owns.
SELECT clothes_id FROM teams_clothes WHERE team_id = 4 and this return (35, 45, 55)
How can I create a query so that it returns (13)? I've tried things like NOT EXISTS IN but I think the GROUP BY players_clothes.clothes_id part gets in the way

Answer 1

I suggest
select * from A where team_id = $team_id join B on B.a_id = A.id
where not exists
(
select 1 from C where C.clothes_id = B.clothes_id and team_id = $team_id
)
Basically, we find all As who are on their team and for each A join to all clothing they wear, and then only return the row IF we can't find indication in table C that the clothing is on our team (this covers not existent in C and exists but in the wrong team on C)

Answer 2

This should do the trick:
SELECT b.a_id, b.clothes_id
FROM
b INNER JOIN a
ON b.a_id = a.id
LEFT OUTER JOIN c
ON a.team_id = c.team_id
WHERE
c.clothes_id = NULL
The thought is to do an outer join on the combination of tables A/B against table C. And then only look for the cases where c.clothes_id is NULL, which would represent those cases where there is no relational match on the outer join (i.e. the clothes item is not approved for that user's team).

Answer 3

Not sure if this is too late for you, but I'd change the database model itself to make this situation impossible in the first place:
("Unimportant" fields omitted for brevity, including surrogate keys such as PLAYER_ID.)
Note how TEAM_ID migrates through the identifying relationship from TEAM to PLAYER, and then to the PLAYER_ARTICLE, where it merges with the same field migrated through the TEAM_ARTICLE. Since there is only one physical TEAM_ID field in the PLAYER_ARTICLE table, you can never insert a row that would reference different teams.
To put it in more abstract terms: this is a diamond-shaped dependency, where TEAM is at the top and PLAYER_ARTICLE at the bottom of the diamond. The merger at the bottom (enabled by the usage of identifying relationships) ensures sides must always point to the same top.
Your example data would be represented like this...
PLAYER:
TEAM_ID PLAYER_NO
4 1 -- Tom
5 1 -- Robo
4 2 -- Bob
TEAM_ATRICLE:
TEAM_ID ARTICLE_ID
4 35
4 45
4 55
5 65
PLAYER_ARTICLE:
TEAM_ID PLAYER_NO ATRICLE_ID
4 1 13 -- Tom: this is impossible (FK violation).
4 2 35 -- Bob
4 2 45 -- Bob