MYSQL Join之谜：同时inner和left join

Question

我有以下表格：

Schools
Teachers
Courses
XRefSchoolsTeachers
XRefCoursesTeachers

现在我正在尝试获取提供该课程的大学所有教师的名单，这些教师不教授该课程。到目前为止，我有：

SELECT *
FROM Courses
INNER JOIN XRefSchoolsTeachers
    ON Courses.SchoolID = XRefSchoolsTeachers.SchoolID

这给了我提供该课程的学校所有教师的 ID，但现在我需要删除所有与 XRefCoursesTeachers 中该课程 ID 不相符的教师 ID。我查看了another question here 关于如何删除不在另一个列表中的内容，我需要一个左连接。但我觉得我也需要一个内部加入，这样我才能得到那所学校的老师，他们已经不在名单上>

例如

SELECT *
FROM Courses
INNER JOIN XRefSchoolsTeachers
    ON Courses.SchoolID = XRefSchoolsTeachers.SchoolID
LEFT JOIN XRefCoursesTeachers
    ON (XRefCoursesTeachers.TeacherID = XRefSchoolsTeachers.TeacherID
     AND XRefCoursesTeachers.CourseID = Courses.ID)
WHERE Courses.ID = ? AND XRefSchoolsTeachers.TeacherID IS NULL

会给我任何其他学校的任何其他课程的所有老师 - 这不是我想要的。我想要所有可以教这门课程但不能教的老师。

就像我需要在XRefCourseTeachers.CourseID = Courses.ID 上进行内部联接，然后使用TeacherID 在XRefCourseTeachers 的同一实例上进行左联接，这样我就可以挑选出NULL 结果。但我不知道该怎么做。

这怎么可能？我是否采取了正确的方法？

Answer 1

SELECT *
FROM Courses
INNER JOIN XRefSchoolsTeachers
    ON Courses.SchoolID = XRefSchoolsTeachers.SchoolID
left join XRefCoursesTeachers
    on XRefCoursesTeachers.TeacherID = XRefSchoolsTeachers.TeacherID
where 
    XRefCoursesTeachers.TeacherID is null
    and
    Cousers.ID = ?

或

SELECT *
FROM Courses
INNER JOIN XRefSchoolsTeachers
    ON Courses.SchoolID = XRefSchoolsTeachers.SchoolID
where 
    XRefCoursesTeachers.TeacherID not in (
        select TeacherID
        from XRefCoursesTeachers
        where XRefCoursesTeachers.CourseID = Courses.ID
    )
    and
    Courses.ID = ?

Answer 2

找到解决方案：

SELECT *
FROM Courses
INNER JOIN XRefSchoolsTeachers
    ON Courses.SchoolID = XRefSchoolsTeachers.SchoolID
LEFT JOIN XRefCoursesTeachers
    ON (XRefCoursesTeachers.TeacherID = XRefSchoolsTeachers.TeacherID AND XRefCoursesTeachers.CourseID = Courses.ID)
WHERE 
        XRefCoursesTeachers.TeacherID IS NULL
    AND
        Cousers.ID = ?