Sql加入多列表返回兩列的產品

我想在asp.net中生成一個sql server數據庫的報告，我得到一些列作爲兩列產品的結果。下面是代碼Sql加入多列表返回兩列的產品

comm.CommandText = "SELECT Count(Courses.CourseID) AS CourseCount, Count(Students.StudentID) AS StudentCount, Schools.Name, Schools.StartDate, Schools.SchoolFees " + 
       "FROM Schools" + 
       "LEFT JOIN Courses ON (Schools.SchoolID = Courses.SchoolID)" + 
       "LEFT JOIN Students ON (Schools.SchoolID = Students.SchoolID) " + 
       "WHERE Schools.Active = 1 " + 
       "GROUP BY Schools.Name, Schools.StartDate, Schools.SchoolFees";

當運行的代碼，其結果顯示，但對於「CourseCount」和「StudentCount」的列顯示一個值，該值是每個單獨的柱的產物。「CourseCount」通常是288，「StudentCount」是38，但是當我運行代碼時，「CourseCount」和「StudentCount」顯示10944爲38 x 288.

無論如何，我可以讓他們顯示正確的值？

來源

2016-05-05 elfico

使用所有行數，以不同值的數改變你的代碼而已，應該返回你期望返回

comm.CommandText = "SELECT Count(DISTINCT Courses.CourseID) AS CourseCount, Count(DISTINCT Students.StudentID) AS StudentCount, Schools.Name, Schools.StartDate, Schools.SchoolFees " + 
      "FROM Schools" + 
      "LEFT JOIN Courses ON (Schools.SchoolID = Courses.SchoolID)" + 
      "LEFT JOIN Students ON (Schools.SchoolID = Students.SchoolID) " + 
      "WHERE Schools.Active = 1 " + 
      "GROUP BY Schools.Name, Schools.StartDate, Schools.SchoolFees";

的結果是技術上是正確的，如果所有的學校都有課程的結果，並且所有課程都有學生

來源

2016-05-05 13:46:56 rossquan

效果很好！非常感謝@rossquan。 – elfico

如上所述，您是如何使用COUNT（），您是要求它計算所有，這就是爲什麼它返回這麼多。只需計算您想要計算的兩個值即可使用計數。

來源

2016-05-05 13:59:00 user6295925

這可能表現比重複計數方法越好..

comm.CommandText = 
    "SELECT cc.CourseCount, sc.StudentCount, Schools.Name, Schools.StartDate, Schools.SchoolFees " + 
    "FROM Schools" + 
    "OUTER APPLY (SELECT Count(Students.StudentID) StudentCount FROM Students WHERE Students.SchoolID = Schools.SchoolID) sc " + 
    "OUTER APPLY (SELECT Count(Courses.CourseID) CourseCount FROM Courses WHERE Courses.SchoolID = Schools.SchoolID) cc " + 
    "WHERE Schools.Active = 1 ";

來源

2016-05-05 14:09:31 JamieD77

Sql加入多列表返回兩列的產品

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