These questions were inspired by the talk WAT that makes fun of some Javascript and Ruby "features". I've been reading The Art of Postgresql and thought SQL NULLs deserved a similar treatment. Please enjoy this quiz that sheds some light on the best NULL semantics in SQL. All examples were run in Postgres. Other RDBMSs may differ slightly.
employees +----+-------+------------+ | id | name | manager_id | +----+-------+------------+ | 1 | Alice | NULL | | 2 | Bob | 1 | | 3 | Cara | 2 | | 4 | Dana | NULL | +----+-------+------------+
SELECT id, name FROM employees WHERE manager_id != 1;