方法)外部连结
- 使用join
- 电影没有分类
select f.film_id, f.title from film as f left join film_category as fc on f.film_id = fc.film_id where fc.category_id is null;
select f.film_id, f.title from film as f left join film_category as fc on f.film_id = fc.film_id where fc.category_id is null;