I recenly learned that it's possible to to join a SQL table with itself.

Consider the following table. We would like to find the name of the employees who make more money than their manager.

Table: Employees

The below query would join Employees with itself.

SELECT * FROM Employees e
JOIN Employees m ON e.manager_id = m.id;

This would be the output.

By editing the SELECT statement, and adding a WHEREstatement, we accomplish our goal.

SELECT e.name FROM Employees e
JOIN Employees m ON e.manager_id = m.id
WHERE e.salary > m.salary;

Voila!