Question

这是我的表

    UserDetail

Id  UserId CourseId  SubjectId TeacherCode   RDate        status
 1  1      1          1         1          08/02/2016     Waiting
 2  1      1          1         2          08/01/2016     Recceived
 3  1      1          1         3          08/02/2016     Processed
 4  1      1          2         1          08/03/2016     Recceived
 5  1      1          2         2          08/04/2016     Processed
 6  1      2          1         3          08/05/2016     Processed
 7  1      2          2         1          08/06/2016     Processed

用户可以有多个课程，多个科目。一个教师可以教多个科目。我想从表格中获取所有栏目，基于不同的用户标识，课程和主题。在7行中，只要显示4行。下面的任何一条记录

Id  UserId CourseId  SubjectId TeacherCode   RDate        status
 1  1      1          1         1          08/02/2016     Waiting
 2  1      1          1         2          08/01/2016     Recceived
 3  1      1          1         3          08/02/2016     Processed

如果我们选择教师代码1，则rdate为08/02/2016并且状态为Waiting 既不接受也不处理。下面的任何一个

Id  UserId CourseId  SubjectId TeacherCode   RDate        status
4   1      1          2         1          08/03/2016     Recceived
5   1      1          2         2          08/04/2016     Processed

怎么做？

Answer 1

您必须知道要选择哪些区别的数据。第一排？最后一行？

因为每组有区别的数据都是多行，所以你应该选择你想要的那一行。

我假设您想要每个特定组的第一行。你可以这样做：

Select first(Id) AS Id, first(UserId) AS UserId, first(CrouseId) AS CourseId, first(SubjectId) AS SubjectId, first(TeacherId) AS TescherId,first(RDate) AS RDate, first(status) as status
FROM UserDetail
Group By UserId, CourseId, SubjectId

在sql2005 +中，如下所示：

 WITH temp AS  (
SELECT *, 
       ROW_NUMBER() OVER(PARTITION BY UserId,CourseId,SubjectId ORDER BY Id) AS rn FROM UserDetail)
SELECT t.*
FROM temp t
WHERE t.rn = 1

或者您可以使用内部选择而不是WITH：

来实现

SELECT *
FROM (SELECT *, 
       ROW_NUMBER() OVER(PARTITION BY UserId,CourseId,SubjectId ORDER BY Id) AS rn FROM UserDetail)
WHERE rn = 1

如何为多列分组时获取所有列？

1 个答案: