DBMS Functional Dependencies

Question

Will a single attribute key considered as a prime attribute as well?

I know If it is a compound key like (ABC) then my prime attribute set would be {A,B,C,AB,BC,AC}

But if I have only 1 Candidate key in my relation (A) then will A also be a prime attribute or not?

Also if multiple single attribute keys are there then what happens (Say {A}, {B} are both candidates) with the prime attributes?

Answer 1

If A is only one candidate key then A, AB,AC will be prime attributes

Comments

Part of the candidate key is a prime attribute, so I dont think AB and AC are going to be prime attributes.

---

Exactly

Answer 2

• Prime attribute = any attribute that is part of some candidate key.

• Non-prime attribute = not part of any candidate key.

So if an attribute alone forms a candidate key, it is 100% prime, because it is itself a full candidate key

Answer 3

If A is the candidate key of the relation, then A itself is called as the prime attribute. Not the other attributes{B, C} in the super keys- AB, AC are called as Prime Attributes.

 

But if D -> A, then D would also be called as Prime Attribute.

Because, by definition prime attribute means part of candidate key, but not Super-key.

If the definition was w.r.t Super-key, then every attribute in the relation would be called as a prime attribute right? But that is not the case.

 

I hope it is clear to you now!