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我有一个团队、学校和作业的数据库。选择作业后，学校（无论如何都是其用户）可以将团队添加到作业中，以便他们可以开始处理作业。ER 图如下所示： 数据库的ER图 重要提示：即使数据库的设置另有说明，团队<-> 分配关系也是 1:N。一个团队只能完成一项任务。这是通过 ORM 系统控制的。

现在有一个问题：数据库中有团队在处理不属于他们学校的作业：学校选择作业，创建了一个团队并删除了他们的作业选择。我需要找到属于这种情况的学校（id、name）。

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？

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1 回答 1

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其中一个应该可以工作，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
  )
于 2012-10-14T22:02:02.843 回答