Composite Key

Hello, just wondered if anybody could either tell me the answer or point me in the right direction to the following question.

I have a table that maps Users to Requirements

The following is Valid

Where User = Jon, Bob and Requirements = 1, 2....

User Requirements
Jon 1
Jon 2
Bob 1
Jon 3
Bob 2

The following is not Valid

Jon - 1
Jon - 2
Bob - 1
Jon - 1

So I basically need to know how I can enable the above constraint.

Any help is much appreciated

Jon
Not to worry. Solved it..