第一步子查询：从category选出电影分类名称name为'action'的category_id，即 (select category_id from category where name='action') 第二步子查询，从film_category中选出category_id等于第一步子查询category_id的film_id，即 (select film_id from film_category where category_id in (第一步子查询)) 最后，基于前两步子查询，从film选出满足条件的select title,description select title,description from film where film_id in (select film_id from film_category where category_id in (select category_id from category where name='action'))