選擇部門名稱預查詢requiste

Question

我有三個表，如下圖所示：

Courses(
    Number: integer, 
    DeptName: string, 
    CourseName: string, 
    Classroom: string, 
    Enrollment: integer) 

Departments(
    Name: string, 
    ChairmanPID: string) 

PreReq(
    Number: integer, 
    DeptName: string, 
    PreReqNumber: integer, 
    PreReqDeptName: string) 

，我必須找到哪些部門有，在其他部門的先決條件課程？

Answer 1

嘗試這個

Select D.Name,C.CourseName, P.DeptName 
    From Department D 
    INNER JOIN Courses C ON C.DeptName=D.DeptName 
    INNER JOIN PreReq P ON P.PreReqDeptName=D.DeptName AND P.DeptName <> D.DeptName 

Answer 2

SELECT DISTINCT p.DeptName 
FROM PreReq p 
WHERE p.DeptName <> p.PreReqDeptName