题解 | #使用join查询方式#

# category_id isNull


#### 不用join
# select film_id, title
# from film
# where film_id not in (
#     select film_id from film_category 
# )


#### 使用join
# 左连接电影信息表和电影分类表 ffc
# select 
#     f.film_id as film_id,
#     f.title as title,
#     fc.category_id as category_id
# from film f left join film_category fc on f.film_id=fc.film_id

# 选择category_id is null的记录
select 
    ffc.film_id,
    ffc.title
from (
    select 
        f.film_id as film_id,
        f.title as title,
        fc.category_id as category_id
    from film f left join film_category fc on f.film_id=fc.film_id
) ffc 
where ffc.category_id is null