Question

我有以下数据库：

Prof(profBadge, profName, Department) Course(courseCod, courseName, profBadge, area) Class(classCode, date, courseCod, numberOfStudents)

以下要求：对于只有区域数据库的每位教授，数据库都会显示徽章编号和平均学生人数最多的课程。

Create view badgeList(profBadge, courseCod) as
SELECT DISTINCT profBadge, courseCod
FROM Coure
WHERE (profBadge NOT IN (SELECT profBadge
                   FROM Course
                   WHERE Area <> 'database'));

Create view avgLessons(AvgStud, courseCod) as
SELECT AVG(numberOfStudents), courseCod
FROM class
GROUP BY courseCod;

Create view MaxStudent(maxStu, profBadge) as
select max(med.avgStud), el.profBadge
from avgLessons med, badgeList el
where med.courseCod= el.courseCod
group by el.profBadge;

select DISTINCT MS.profBadge, MS.MAXSTU, Corso.CODCORSO
from MaxStudent MS, course, class
where MS.profBadge = course.profBadge and MS.maxStu = class.numberOfStudents and course.courseCod = class.courseCod;`

Answer 1

我不知道我是否看到了你想要达到的目标，但下面的代码返回了profBadges，只返回那些平均学生人数最多的courseNames（通过所属类的数量计算）。

SELECT profBadge,
  courseName
FROM
  (SELECT C.profBadge,
    C.courseName,
    SUM(CL.numberOfStudents)                                                      /COUNT(CL.classCode)  AS Avg_Students_Num,
    ROW_NUMBER () OVER (PARTITION BY C.profBadge ORDER BY SUM(CL.numberOfStudents)/COUNT(CL.classCode)) AS Rank
  FROM Course C
  LEFT JOIN Class CL
  ON CL.courseCod=C.courseCod
  GROUP BY C.courseName,
    C.profBadge
  )
WHERE Rank=1

Answer 2

这不是一件容易的事。如上所述，请一步一步地完成。

第1步：只有区域和数据库课程的教授。像你一样使用NOT IN是解决这个问题的一种方法。另一个（通常是最快的）是聚合。

SELECT profBadge
FROM Course
GROUP BY profBadge
HAVING MIN(Area) = 'database' AND MAX(Area) = 'database';

第2步：每个课程的平均学生人数，正如您自己展示的那样。

SELECT courseCod, AVG(numberOfStudents)
FROM class
GROUP BY courseCod;

第3步：将两者结合起来。您选择profBadge在第一组中的课程（从步骤1开始查询），并按平均学生数量（您必须从步骤2加入查询）对其进行排名。

SELECT courseCod, courseName, profBadge, area
FROM
(
  SELECT 
    c.courseCod, c.courseName, c.profBadge, c.area,
    RANK() OVER (PARTION BY c.profBadge ORDER BY av.avgNum DESC) AS rn
  FROM Course c
  JOIN
  (
    SELECT courseCod, AVG(numberOfStudents) AS avgNum
    FROM class
    GROUP BY courseCod
  ) av ON av.courseCod = c.courseCod
  WHERE c.profBadge IN
  (
    SELECT profBadge
    FROM Course
    GROUP BY profBadge
    HAVING MIN(Area) = 'database' AND MAX(Area) = 'database'
  )
)
WHERE rn = 1;

对团体进行锻炼

2 个答案: