SELF JOIN — an employee and their manager

I join the table to itself using two aliases. LEFT JOIN also keeps people without a manager.

-- employees(id PRIMARY KEY, name, manager_id)
SELECT e.name AS employee, m.name AS manager
FROM employees AS e
LEFT JOIN employees AS m ON m.id = e.manager_id;

To be precise: INNER JOIN returns only people with a match. Here, no manager gives NULL in the manager column.

Pitfall: a filter WHERE m.name = 'Anna' drops the rows without a match. With outer joins it matters whether a condition goes into ON or WHERE.