What is candidate key?

What is meant by candidate key?

Candidate key is a single key or a group of multiple keys that uniquely identify rows in a table. A Candidate key is a subset of Super keys and is devoid of any unnecessary attributes that are not important for uniquely identifying tuples. The value for the Candidate key is unique and non-null for all tuples.

What is candidate key & primary key?

Primary Key is a unique and non-null key which identify a record uniquely in table. A table can have only one primary key. Candidate key is also a unique key to identify a record uniquely in a table but a table can have multiple candidate keys.

Why do we use candidate key?

Candidate key means exactly the same thing as primary key. All candidate keys serve the same purpose: to ensure data integrity by preventing duplicate data. It's perfectly sensible for a table to have more than one candidate key enforced in it if that's necessary to ensure some data is not duplicated.