Question

I’ve ran into an issue that I can’t seem to solve.

Say for instance that I have a table with upcoming videogame releases:

GAME
game_ID | title             
-----------------------------
1       | Super Mario
2       | Final Fantasy XIII

And then I’ve got a table with releasedates (different dates for ps3 and xbox360 just for the sake of the argument):

RELEASES
game_ID | releasedate | platform
---------------------------------
1       | 20-04-2010  | Wii
2       | 23-03-2010  | PS3
3       | 20-03-2010  | Xbox360

Now, I have put game_ID as the primary key in the table “GAME”. And game_ID is also a foreign key in the table “RELEASES”. What should I have as the primary key in the latter? It seems rather unnecessary to create yet another ID-key in the “RELEASES”-table?

Can I somehow use game_ID and platform together to create the primary-key? If so, how would the SQL look like?

Answer 1

You can create a composite key that consists of game_id and platform just like you create a primary key that consists of only one column:

PRIMARY KEY(game_id, platform)