从子查询SQL Server 2014获取正确的数据

Question

我正在努力找到我的数据库中的教师数量，这些教师能够教授由名为“Ian Goldman”的教师授课的课程。

以下是涉及的关系的模式：

/*Instructors that can teach the courses that have been taught by Ian Goldman*/
select 
    InstructorNo
from 
    AreasOfCourse, AreasOfInstructor, 
    (/*courses that have been taught be Ian Goldman*/
     select DISTINCT CourseNo
     from CourseSections
     where InstructorNo = (select InstructorNO
                           from Instructors
                           where FirstName = 'Ian' 
                             and LastName = 'Goldman')
    ) AS GoldmansCourses
where 
    AreasofCourse.CourseNo = GoldmansCourses.CourseNo 
    and AreasofInstructor.AreaName = AreasOfCourse.AreaName
group by 
    InstructorNo
having 
    COUNT(DISTINCT AreasofCourse.CourseNo) = COUNT((GoldmansCourses.CourseNo)

当我查询数据库（即Goldman教授的课程）时，GoldmansCourses子查询返回与2个不同课程的关系。当我在最后一行打电话给COUNT((GoldmansCourses.CourseNo))时，我期待得到2回。

然而，实际发生的是我在每个分组中给出了元组的数量（即查询在from子句中给出了关于笛卡尔积的信息，而不是GoldmansCourses关系中的课程数量）。

我该如何解决这个问题？我需要访问原始子查询GoldmansCourses，而不是FROM子句计算的笛卡尔积中的列。

Answer 1

 SELECT InstructorNo
 FROM AreasOfInstructor AI
 JOIN AreasOfCourse  AC
   ON AI.Course = AC.Course
 LEFT JOIN GoldmansCourses GC
   ON AI.Course = GC.Course
 WHERE 
     GC.Course IS NOT NULL
 GROUP BY InstructorNo
 HAVING  COUNT(DISTINCT AreasofCourse.CourseNo) = COUNT((GoldmansCourses.CourseNo)