- a simple or composite key that is unique and minimal
- unique – no two rows in a table may have the same value at any time
- minimal – every column must be necessary for uniqueness
- For example, for the entity
Employee(EID, First Name, Last Name, SIN, Address, Phone, BirthDate, Salary, DepartmentID)
Possible candidate keys are EID, SIN
FirstName and Last Name – assuming there is no one else in the company with the same name, Last Name and DepartmentID – assuming two people with the same last name don’t work in the same depart ment.
EID, SIN are also candidate keys