between primary and super key
Primary Key: is
the columns you choose to maintain uniqueness in a table. Here in Employee
table you can choose either EmployeeID or SSN columns, EmployeeID is
preferable choice, as SSN is a secure value.
Super Key: If
you add any other column/attribute to a Primary Key then it become a super key,
like EmployeeID + FullName is a Super Key.
Check this useful article to know more details