A relational database management system allows the temporary or permanent joining of data table based on a common field (a primary and foreign key). Each row, record or instance in a database has a fixed set of attributes or fields. Each table has a primary key that uniquely identifies each record. The table may also contain a foreign key, which is identical to a primary key in an external table. A relational join is achieved by matching the values of the foreign key to the corresponding values in the primary key of the external table.