You don't make a candidate key, you select candidate keys from your
normalized data. Use one or more candidate keys to make a Primary
Key - which must be unique. Often candidate keys which the customer
has told you will absolutely never change, get changed..
There are proponents of natural keys - where candidate keys play a
role. There also proponents of the Autonumber surrogate keys. I'm
one of the latter. Just be sure not to use an Autonumber datatype for
any other purpose than as a surrogate primary key.
HTH
