MYSQL加入拼圖：內部和左連接在同一時間

Question

我有以下表格：

Schools 
Teachers 
Courses 
XRefSchoolsTeachers 
XRefCoursesTeachers 

現在我想在課程的，所提供的大學獲得所有教師的列表，它不在教這門課程。到目前爲止，我有：

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

這給了我所有的老師的ID在該課程在所提供的學校，但現在我要刪除哪些是不反對的，該ID老師的所有ID當然在XRefCoursesTeachers。我看着another question here關於如何刪除不在另一個列表上的東西，我需要一個左連接。但我覺得我還需要一個內部加入，以便我只從該學校獲得不在列表中的教師> <

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 

會給我任何其他學校的其他任何課程的所有老師 - 不是我想要的。我希望所有可以教導這個課程的老師，但不是。

它就像我需要一個內部聯接上XRefCourseTeachers.CourseID = Courses.ID，然後左連接上使用TeacherID，這樣我可以挑出NULL結果XRefCourseTeachers相同的實例。但我不知道該怎麼做。

這怎麼可能？我採取了正確的方法嗎？

Answer 1

找到了解決辦法：

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 = ? 

Answer 2

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 = ?