题解 | #使用join查询方式找出没有分类的电影id以及其电影名称#

使用left join 连接表，使得以电影票为左边都有数据，

select t1.film_id,t1.title,t3.category_id
from film t1 left join film_category t2 on 
t1.film_id = t2.film_id 
left join category t3 on 
t2.category_id = t3.category_id 

此时没有类别的电影为第三行，t3.category_id is null过滤即可,即答案为

select t1.film_id,t1.title
from film t1 left join film_category t2 on 
t1.film_id = t2.film_id 
left join category t3 on 
t2.category_id = t3.category_id 
where t3.category_id is null