SELF JOIN for Hierarchies

A self join joins a table to itself. This is common when rows relate to other rows in the same table, such as employees and managers.

SELECT e.name AS employee_name, m.name AS manager_name
FROM employees AS e
LEFT JOIN employees AS m
  ON e.manager_id = m.id

The `employees` table appears twice with different aliases. One copy represents the employee, and the other represents the manager.

This pattern is useful for org charts, parent-child relationships, and tree-like data.