MySQL - 任意行的 count()

Question

我有一个这样的erd:

erd

我希望所有 Actor 都与一位特定导演合作。
这是我的查询:

    SELECT 
    p.first_name, p.last_name, COUNT(r.movie_id) as working_number
FROM
    person p
          LEFT JOIN
    roles r ON r.person_id = p.id
WHERE
    r.movie_id IN (SELECT 
            r.movie_id
        FROM
            roles r
        WHERE
            role_type = 'Director'
                AND person_id = (SELECT 
                    id
                FROM
                    person
                WHERE
                    first_name = 'Quentin'
                        AND last_name = 'Tarantino'))
                        and r.role_Type = "Actor"
GROUP BY p.id;

这会检索工作编号大于 1 的 Actor 。
我也想要其他 Actor ，即使工作人数为 0。

Answer 1

您需要多个左连接，person 和 role 两次:

SELECT p.first_name, p.last_name, COUNT(pd.id) as working_number
FROM person p
LEFT JOIN role r ON r.person_id = p.id AND r.role_Type = 'Actor'
LEFT JOIN role rd ON rd.movie_id = r.movie_id AND rd.role_type = 'Director'
LEFT JOIN person pd ON pd.id = rd.person_id AND pd.first_name = 'Quentin' AND pd.last_name = 'Tarantino'
GROUP BY p.id, p.first_name, p.last_name