MySQL三通三角查询

Question

我有一个团队，学校和作业的数据库。选择作业后，学校（无论如何用户）可以在作业中添加一个团队，以便他们可以开始分配作业。 ER图如下所示： 重要提示：即使数据库的设置另有建议，团队＆lt; - ＆gt;赋值关系为1：N。一个团队只能处理一项任务。这是通过ORM系统控制的。

现在这里有一个问题：数据库中有团队负责不属于他们学校的作业：学校选择作业，创建团队并删除他们的作业选择。我需要找到这种情况的学校（身份证，姓名）。

到目前为止，我设法提出的最佳查询是：

SELECT schools.school_id, schools.name
FROM schools
LEFT JOIN teams ON schools.school_id = teams.school_id
LEFT JOIN assignment_teams ON teams.team_id = assignment_teams.team_id
LEFT JOIN assignment_schools ON schools.school_id = assignment_schools.school_id
WHERE assignment_teams.assignment_id != assignment_schools.assignment_id;

但是当我手动检查结果时它不起作用。我正在寻找的正确查询是什么？

Answer 1

其中一个应该可行，但我不知道哪个是最快的：

1.   SELECT school_id
     FROM teams
     INNER JOIN assignment_teams ON teams.team_id = assignment_teams.team_id
     LEFT JOIN assignment_schools ON assignment_schools.school_id = teams.school_id AND  assignment_schools.assignment_id = assignment_teams.assignment_id
     WHERE assignment_schools.school_id IS NULL
   

2. SELECT school_id
     FROM teams
     INNER JOIN assignment_teams ON teams.team_id = assignment_teams.team_id
     WHERE assignment_id NOT IN (
       SELECT assignment_id
         FROM assignment_schools
         WHERE assignment_schools.school_id = teams.school_id
     )
   

3. SELECT school_id
     FROM teams
     INNER JOIN assignment_teams ON teams.team_id = assignment_teams.team_id
     WHERE NOT EXISTS (
       SELECT *
         FROM assignment_schools
         WHERE assignment_schools.school_id = teams.school_id
         AND assignment_schools.assignment_id = assignment_teams.assignment_id
     )