A super key with no redundant attribute is known as candidate key. Candidate keys are selected from the set of super keys, the only thing we take care while selecting candidate key is: It should not have any redundant attributes. That’s the reason they are also termed as minimal super key.
There are two candidate keys in above table:
Note: A primary key is being selected from the group of candidate keys. That means we can either have Emp_Id or Emp_Number as primary key.