If you've taught SQL or learned it from a course, you've almost certainly met Sakila. The little DVD rental database has been the go-to sample schema for MySQL and MariaDB tutorials for nearly two decades. It's clean, well-normalized, and comes pre-...

Most SQL developers hear the same rule early: always prefer INNER JOIN over correlated subqueries, because subqueries create an N+1 performance problem. That rule is useful, but it is not always true. I tested this on four engines MySQL, Oracle, P...