Candidate key

It is important to have an attribute in a table which uniquely identifies a row is known as a candidate key. This attribute has values which are unique. Let consider the table airport.

Airport
 
The value of the attribute Airlineno is unique in each row. So this is known as candidate key. This is also known as surrogate key.

The value of the attribute Airlineno is unique in each row. So this is known as candidate key. This is also known as surrogate key.