还有哪些老师正在教授John Cullen.SQL教授的课程

Question

我有多个表但是对于这个查询只需要两个表，即Faculty和CourseSection。 我尝试过以下但是失败了。如果有人可以提供帮助。

Select faculty.firstname,faculty.lastname,CourseSection.facid,courseID
from CourseSection,faculty
where CourseSection.facid in(
Select  CourseSection.CourseID 
from CourseSection
where CourseSection.facid =Faculty.facid and firstname='John' AND lastname='Cullen')

Answer 1

您应该在表格之间使用左连接（假设您的表格与CourseSection.facid = faculty.facid相关）

  Select 
        faculty.firstname
        ,faculty.lastname
        , CourseSection.facid
        , CourseSection.courseID
  from CourseSection 
  LEFT JOIN  faculty on CourseSection.facid = faculty.facid
  where CourseSection.facid in (
  Select  CourseSection.CourseID 
      from CourseSection
      where CourseSection.facid =Faculty.facid 
      and firstname='John' AND lastname='Cullen')

Answer 2

您需要Faculty CourseSection FacID加入CourseSection一次，找到'John Cullen'教授的课程，再次加入CourseID Faculty查找所选课程的所有教师（我想不包括“John Allen”），最后再次使用select f2.facid, f2.firstname,f2.lastname, c2.courseID from Faculty f join CourseSection c on f.facid = c.facid join CourseSection c2 on c.CourseID = c2.CourseID join Faculty f2 on c2.facid = f2.facid and f.facid <> f2.facid where f.FirstName = 'John' and f.LastName = 'Cullen'; 加入教师的数据（点击 here 演示）：

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