Lets say we have 3 tables (actually I have 2 at the moment, but this example might illustrate the thought better):

[Person]

• ID: int, primary key
• Name: nvarchar(xx)

[Group]

• ID: int, primary key
• Name: nvarchar(xx)

[Role]

• ID: int, primary key
• Name: nvarchar(xx)

[PersonGroupRole]

• Person_ID: int, PRIMARY COMPOSITE OR NOT?
• Group_ID: int, PRIMARY COMPOSITE OR NOT?
• Role_ID: int, PRIMARY COMPOSITE OR NOT?

Should any of the 3 ID's in the relation PersonGroupRole be marked as PRIMARY key or should they all 3 be combined into one composite?? whats the real benefit of doing it or not?

I can join anyways as far as I know, so Person JOIN PersonGroupRole JOIN Group gives me which persons are in which Groups etc.

I will be using LINQ/C#/.NET on top of SQL-express and SQL-server, so if there is any reasons regarding language/SQL that might make the choice more clear, thats the platform I ask about.

Looking forward to see what answers pops up, as I have thought of these primary keys/indexes many times when making combined ones.