Unique keys are an alternative to the primary key of the relation.

A unique key is a data attribute or combination of attributes in a database table that uniquely identifies each record. It ensures that no two records in the table have the same values for the specified key, providing a way to uniquely and efficiently identify each row in the database.

A column or group of columns known as a unique key serves as a unique identifier for each record in a table. Every value in this Key must be distinct. A primary key cannot have any null values, but a unique key can have one, which is how it differentiates from a primary key.