我有一些包含电影、 Actor 和类别数据的相关表。我试图总结每个 Actor 在特定类别中的电影长度。
以下是我必须尝试在结果中包含类别 ID 子查询的总和:
SELECT actor.actor_id, (SELECT SUM(length) from film WHERE category_id=14) total
FROM actor
JOIN film_actor USING(actor_id)
JOIN film USING(film_id)
JOIN film_category USING(film_id)
JOIN category USING(category_id)
GROUP BY actor.actor_id
ORDER BY total DESC
但是我的 total
列只包含所有 NULL 值。
此查询有效,但不包括在此类别中观看过 0 分钟电影的 Actor :
SELECT actor.actor_id, SUM(film.length) as total
FROM actor
JOIN film_actor USING(actor_id)
JOIN film USING(film_id)
JOIN film_category USING(film_id)
JOIN category USING(category_id)
WHERE category_id = 14
GROUP BY actor.actor_id
最佳答案
您需要一个外连接,并且类别的条件属于外连接的 on 子句:
select a.actor_id,
sum(f.length) as total
from actor a
join film_actor fa
on a.actor_id = fa.actor_id
join film f
on fa.film_id = f.film_id
left join film_category fc
on fc.film_id = f.film_id
and fc.category_id = 14
group by a.actor_id
关于mysql - SQL:选择子查询的总和,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/31361903/