mysql通过有来计数组

Question

我有这张表：

Movies (ID, Genre)

一部电影可以有多种类型，因此 ID 并不特定于某个类型，而是多对多的关系。我想要一个查询来查找恰好有 4 种类型的电影总数。我当前的查询是

  SELECT COUNT(*) 
    FROM Movies 
GROUP BY ID 
  HAVING COUNT(Genre) = 4

但是，这会返回 4 的列表而不是总和。如何获取总和而不是 count(*) 列表？

Answer 1

一种方法是使用嵌套查询：

SELECT count(*)
FROM (
   SELECT COUNT(Genre) AS count
   FROM movies
   GROUP BY ID
   HAVING (count = 4)
) AS x

内部查询获取恰好具有 4 个流派的所有电影，然后外部查询计算内部查询返回的行数。

Answer 2

SELECT COUNT(*) 
FROM   (SELECT COUNT(*) 
        FROM   movies 
        GROUP  BY id 
        HAVING COUNT(genre) = 4) t

Answer 3

也许

SELECT count(*) FROM (
    SELECT COUNT(*) FROM Movies GROUP BY ID HAVING count(Genre) = 4
) AS the_count_total

虽然这不是所有电影的总和，但有多少电影有 4 种类型。

所以也许你想要

SELECT sum(
    SELECT COUNT(*) FROM Movies GROUP BY ID having Count(Genre) = 4
) as the_sum_total

Answer 4

怎么样：

SELECT COUNT(*) FROM (SELECT ID FROM Movies GROUP BY ID HAVING COUNT(Genre)=4) a