Sql 对某个房间里某些学生的询问

我正在解决一个问题，使用SQL Oracle。出于某种原因，我得到了13分，而我本应该只得到1分，但教授该课程的讲师却得到了13分。教室里只有一名教师只教3个或更多的学生

问题：

SELECT COUNT(Instructor_Id) AS NumberOfInstructors
FROM Section s, Enrollment e
WHERE s.Section_Id = e.Section_Id
  AND Location = 'L211'
HAVING COUNT(Student_Id) = 
(SELECT COUNT(Student_iD)
FROM Section s, Enrollment e
WHERE s.Section_Id = e.Section_Id
 AND Location = 'L211')
ORDER BY s.Course_No;

NUMBEROFINSTRUCTORS   
-------------------   
13           

NUMBEROFINSTRUCTORS   
-------------------   
1

创建一个查询，以确定在L211教室讲授的课程部分中教授了3名以上学生的讲师人数

我的代码：

SELECT COUNT(Instructor_Id) AS NumberOfInstructors
FROM Section s, Enrollment e
WHERE s.Section_Id = e.Section_Id
  AND Location = 'L211'
HAVING COUNT(Student_Id) = 
(SELECT COUNT(Student_iD)
FROM Section s, Enrollment e
WHERE s.Section_Id = e.Section_Id
 AND Location = 'L211')
ORDER BY s.Course_No;

NUMBEROFINSTRUCTORS   
-------------------   
13           

NUMBEROFINSTRUCTORS   
-------------------   
1

我的结果：

SELECT COUNT(Instructor_Id) AS NumberOfInstructors
FROM Section s, Enrollment e
WHERE s.Section_Id = e.Section_Id
  AND Location = 'L211'
HAVING COUNT(Student_Id) = 
(SELECT COUNT(Student_iD)
FROM Section s, Enrollment e
WHERE s.Section_Id = e.Section_Id
 AND Location = 'L211')
ORDER BY s.Course_No;

NUMBEROFINSTRUCTORS   
-------------------   
13           

NUMBEROFINSTRUCTORS   
-------------------   
1

预期结果：

SELECT COUNT(Instructor_Id) AS NumberOfInstructors
FROM Section s, Enrollment e
WHERE s.Section_Id = e.Section_Id
  AND Location = 'L211'
HAVING COUNT(Student_Id) = 
(SELECT COUNT(Student_iD)
FROM Section s, Enrollment e
WHERE s.Section_Id = e.Section_Id
 AND Location = 'L211')
ORDER BY s.Course_No;

NUMBEROFINSTRUCTORS   
-------------------   
13           

NUMBEROFINSTRUCTORS   
-------------------   
1

所以我觉得我走的方向是正确的，也许不是，但我觉得这是把所有的老师都加起来了。我把我给的代码弄得乱七八糟，所以如果有人能给我指出正确的方向。我想我需要数一数，因为我想我已经试过了，结果是4，所以我不确定

任何帮助都会很好

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DBMS：我正在使用Oracle SQL Developer

我想这里需要一个子查询。在伪代码中，您正在查找如下查询：

SELECT count(teachers)
FROM
  (SELECT count(students) FROM enrollment where location='L211') AS "numberofstudents"
WHERE numberofstudents > 3

---

我没有测试代码，但在我看来，您缺少了一个条件。您的问题要求您找到“仅在该教室教授3名或3名以上学生的讲师”，但您没有任何条件检查学号>3。试试这个：

SELECT COUNT(Instructor_Id) AS NumberOfInstructors
FROM Section s, Enrollment e
WHERE s.Section_Id = e.Section_Id
AND Location = 'L211'
HAVING COUNT(Student_Id) = 
(SELECT COUNT(Student_iD)
FROM Section s, Enrollment e
WHERE s.Section_Id = e.Section_Id
AND Location = 'L211' AND COUNT(Student_Id) > 3)
ORDER BY s.Course_No;

试试这个：

SELECT COUNT(*) NumberOfInstructors
From (Select Instructor_Id
      FROM Section s
          join Enrollment e
                on e.Section_Id = s.Section_Id 
      WHERE s.Location = 'L211'
      Group By Instructor_Id
      HAVING COUNT(Student_Id) >= 3) Z

---

所以，这是家庭作业，对吗？这是家庭作业，但他做了正确的事情，他“先尝试”，并做了自己的研究。是的，但其他人呢，他们只需谷歌一下就可以找到答案。对该问题的引用搜索将返回此结果作为第一个结果。这一个成功了，我看到我做错了什么，在这个示例中，HAVING COUNT（Student_Id）>=3）需要大于3。它显示的结果是4，而不是1，因为等号fyi