One table in two roles

An employee and their manager are both stored in employees. To show them in one row, do not duplicate data: give the table two aliases and join the relationship.

A self-join is an ordinary JOIN using two aliases for one table. Each alias plays a role; the foreign key links them.

One table in two roles: A self-join is an ordinary JOIN using two aliases for one table. Each alias plays a role; the foreign key links them.