>>>

>>>Employeenumber    Category
>>>12345             1
>>>42535             2
>>>34545             1
>>>34534             1
>>>

>>
>>
>>If I was doing it...this is the model I'd prefer.
>
>Okay, but do you have an opinion about the last example? If so, what opinion? I'm really curious..
>
>A little bit more info: The above is a real example. But in that case the number 12345 can occur twice. It is the combination with category that uniquely identifies the employee.

A primary key would really be the unique identifer - and if it was me I'd have another field for that.