Question

Differentiate between Candidate Key and Primary Key in the context of Relational Database Model.

Answer 1

S. No.	Basis	Primary Key	Candidate Key
1.	Uniqueness	A record in a table can be uniquely identified by its primary key, which is a non-null and unique key. There can only be one main key in a table.	Although a table may have more than one candidate key, a candidate key is also a unique key to identify a record in a table.
2.	Null value	The value of the primary key column cannot be null.	The value of a candidate key column may be null.
3.	Objective	The primary key is the most crucial component of every table or relationship.	A candidate key indicates which key is suitable for use as the primary key.
4.	Relation	A candidate key is the primary key.	A candidate key could be a primary key or not.