The question is that if I have relation R(A,B,C,D) where A is PK and C if Alternate key for that relation, would I, while creating table based on that relation, need to indicate that C is an unique key? What I mean is:

```
create table R (
                 A A's domain,
                 B B's domain,
                 C C's domain,
                 D D's domain,
                 primary key A,
                 unique C 
                )

```

Do I have to specify that C is an unique key for that table even though this key isn't posted from any other table (it is just a canditate key which hasn't been selected to be a primary key?