Primary key is used to uniquely identify every row in the table. Primary keys can be a single field, or a combination of multiple fields.

The conditions that a Primary key must satisfy are the following:

• The primary key must be unique for every record in the table


• The primary key cannot be null (must have a value)


• The primary key’s value should not change


• Only one primary key defined for each table


• If the primary key consists of more than one field, the combination of values must be unique for every record in the table