What is candidate key in SQL

A candidate key is a minimal super key and proper subset of it can not be able to identify each row uniquely(proper subset of it is no longer a super key).

Example 1 Find no. of candidate key

R(A,B,C,D)

A->BC

CD->E

B->D

E->A

Ans

A->ABC

A->ABCD(B->D)

A->ABCDE(E->A)

E->ABCDE

CD->ABCDE

BC->ABCDE

Total no. of candidate key=4