Achievements / Badges system

Question

I have been browsing this site for the answer but I\'m still a little unsure how to plan a similar system in its database structure and implementation.

In PHP and MySQL

Answer 1

I think this is one of those cases where your many-to-many table (Badges_User) is appropriate.
But with a small alteration so that unassigned badges isn't stored.

I assume assigned_at is a date and/or time.
Default is that the user does not have the badges.

Badges     |    Badges_User      |  User
----------------------------------------------
bd_id      |    bd_id            |  user_id
bd_name    |    user_id          |  etc
bd_desc    |    assigned_at      |  
           |                     |

This way only badges actually awarded is stored.
A Badges_User row is only created when a user gets a badge.

Regards
    Sigersted