Question

I searching for many times now on a complex MySQL query.

It’s an achievement system.

Structure of tables is simple and form is symmetric.

The first table (achievements_base) contains the achievements reference : each achievement have :
– an ID (id of the row, auto-increment & unique),
– a code_id (reference of the achievement),
– a rank_id (sub-category of achievement’s code_id),
– and the achievement name (display purposes).

The second table (achievements_user) contains the achievements obtained by the users : each achievement unlocked have :
– an ID (if of the row, auto-increment & unique),
– the code_id (reference of the achievement),
– a rank_id (sub-category of achievement’s code_id),
– and the user id.

The tables syntax is :

achievements_base
id - code_id - rank_id - name
1 - 1 - 1 - foo
2 - 1 - 2 - bar
3 - 1 - 3 - foobar
4 - 1 - 4 - foofoo
5 - 2 - 1 - barbar

achievements_user
id - code_id - rank_id - user_id
1 - 1 - 1 - 1
2 - 1 - 2 - 1
3 - 2 - 1 - 1

I want to display achievements that user don’t have (GROUP BY code_id)

In the table exemple above, for example, expected result is, for the user_id 1 :
3 - 1 - 3 - foobar

But I don’t see how to do that ! I’ve already tried multiples queries.

Sorry for my English, I’m French !

Thanks !

edit, example of one of queries that I’ve tried :

SELECT AB.name
FROM achievements_base AB
RIGHT JOIN achievements_users AU 
ON AU.code_id = AB.code_id AND AU.rank_id = AB.rank_id
WHERE (SELECT COUNT(*) FROM achievements_users AU WHERE AU.user_id = 1) = 0
GROUP BY AB.code_id
ORDER BY AB.code_id ASC

Answer 1

How about the following?

SELECT code_id
FROM achievements_base
WHERE code_id NOT IN
( 
   SELECT code_id
   FROM achievements_user
   WHERE user_id = 1
)
GROUP BY code_id