計數內計數

修訂日期：好吧，感謝您的所有意見，我找出了我做錯了什麼（對不起，夥計們）。我抓住courseID並不是真正的課程。對於我來說，抓住實際的courseName，我必須去課程表。計數內計數

所以現在我有來自課程的註冊和課程號的StudentID需要用來計數。我會試着和你們提供的東西一起工作，看看我能不能拿出結果。編輯：這是我修改後的SQL。這爲我提供了每個學生的全部課程。我越來越有：

SELECT  Count(DISTINCT Course.courseNum), Grades.studentID 
FROM   Grades INNER JOIN 
      Course ON Grades.courseID = Course.courseID 
      GROUP BY Grades.studentID;

終極密碼，以防萬一那些誰照顧：

SELECT COUNT(NumCourses) FROM 
(SELECT  Count(DISTINCT Course.courseNum)AS NumCourses 
FROM   Grades INNER JOIN 
         Course ON Grades.courseID = Course.courseID 
        GROUP BY Grades.studentID 
      HAVING Count(DISTINCT Course.courseNum) = 1) a;

來源

2010-11-28 OneSneakyMofo

你只需要在課程表中添加一個內部連接並在該表上執行having子句。 – IamIC 2010-11-28 09:05:02

如果您覺得您的問題已得到解答，您應該接受答案。 – Martin 2010-11-28 20:39:35

你應該使用投票系統。 – IamIC 2010-11-29 06:14:12

要獲得總數的4+課程的學生，這是SQL：

SELECT COUNT(CourseCount) AS CourseCount 
FROM (
    SELECT StudentID, COUNT(CourseID) AS CourseCount 
      FROM enrollment 
      GROUP BY StudentID 
      HAVING (COUNT(CourseID) >= 4)) AS T

使用第二個查詢獲得學生數量要簡單得多。

來源

2010-11-28 08:26:57 IamIC

試試這個：

select count(studentId), count(courseId) from enrolment group by courseId having (count(courseId) = 2);

來源

2010-11-28 07:55:30

給我所有4s。 – OneSneakyMofo 2010-11-28 08:20:51

SELECT COUNT(*) FROM 
    (SELECT COUNT(*) FROM enrollment 
    GROUP BY studentid HAVING COUNT(*) = 4)

來源

2010-11-28 08:04:09

SELECT COUNT(NumCourses) AS NumStudents, NumCourses FROM (SELECT COUNT(courseID) AS NumCourses FROM enrollment GROUP BY courseID HAVING COUNT(courseID) = 4) As SomeTableAlias

來源

2010-11-28 08:16:18 bowsersenior

我以爲你想要參加四門課程的學生人數。如果要算學生人數和課程的數量，這樣做：

SELECT * FROM (SELECT COUNT(*) AS NumStudents FROM (SELECT DISTINCT studendid FROM enrollment)), (SELECT COUNT(*) AS NumCourses FROM (SELECT DISTINCT courseid FROM enrollment))

來源

2010-11-28 08:31:04

select count(*) 
    from (select student_id from enrollment group by student_id having count(*) = 4)

內部查詢給你誰在完全相同4門課程入選然後我算他們的學生的ID。

來源

2010-11-28 08:34:14

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