输出错误与SQL

Question

我使用以下查询：

Answer 1

下面的查询不完全测试，因为有没有提供采样数据。

SELECT d.LecturerID, d.Name, 
     c.CourseID, c.CourseName, 
     a.Semester, 
     a.percentageOfStudent 
FROM 
     (
      SELECT CourseID, 
        Semester, 
        SUM(CASE WHEN grade >= 6 THEN 1 ELSE 0 END) * 1.0/COUNT(*) * 100.0 percentageOfStudent 
      FROM Exam 
      GROUP BY CourseID, Semester 
      HAVING SUM(CASE WHEN grade >= 6 THEN 1 ELSE 0 END) * 1.0/COUNT(*) * 100.0 < 50 
     ) a 
     INNER JOIN Lecture b 
      ON a.CourseID = b.CourseID AND 
       a.Semester = b.Semester 
     INNER JOIN Course c 
      ON b.CourseID = c.CourseID 
     INNER JOIN Lecturer d 
      ON b.LecturerID = d.LecturerID