Who gets dropped when manager_id is NULL?

Question

Accepted Answer

The table is joined to itself: 'e' represents the employee and 'm' represents the manager. For Bob (manager_id=1), the join finds id=1 which is Alice. Same for Carol. Alice has NULL manager_id, so her row finds no match in the INNER JOIN and is excluded. Use LEFT JOIN if you want Alice in the result with NULL for manager.