Self JOIN

Join a table to itself.

Joining a table with itself is a self JOIN. You use the same table under two different aliases.

SELECT e.name, m.name AS manager
FROM employees e
INNER JOIN employees m ON e.manager_id = m.id;

This query finds each employee's manager.

e.name, m.name AS manager is selected from employees e. employees m is joined on e.manager_id = m.id, keeping only matching rows.

Self JOIN — details

Aliases are mandatory in a self JOIN; otherwise the database cannot tell the two roles apart.

For example, employees e JOIN employees m ON e.manager_id = m.id puts each employee's manager name next to them.

Join employees with itself to find managers.

Show example solution

SELECT e.name, m.name AS manager
FROM employees e
INNER JOIN employees m ON e.manager_id = m.id;

Add the self join

SELECT e.name, m.name AS manager
FROM employees e
____ employees m ON e.manager_id = m.id;

Show answer

SELECT e.name, m.name AS manager
FROM employees e
INNER JOIN employees m ON e.manager_id = m.id;