将具有空值和重复的行压缩为单行

Question

我不确定如何描述我想做什么,所以我将使用一个人为的例子

在SQL Server 2005上,假设我有一个像这样的行的视图,称之为vwGrades:

ID          AssnDate                AssnTxt       Sally       Ted         Bob
----------- ----------------------- ------------- ----------- ----------- -----------
2999        2007-09-22 00:00:00     Homework #1   20          NULL        NULL
2999        2007-09-22 00:00:00     Homework #1   NULL        0           NULL
2999        2007-09-22 00:00:00     Homework #1   NULL        NULL        24
2999        2007-09-22 00:00:00     Final Exam    57          NULL        NULL
2999        2007-09-22 00:00:00     Final Exam    NULL        0           NULL
2999        2007-09-22 00:00:00     Final Exam    NULL        NULL        35

我如何查询它,以便我得到这个,摆脱所有恼人的空值和重复的行？

ID          AssnDate                AssnTxt       Sally       Ted         Bob
----------- ----------------------- ------------- ----------- ----------- -----------
2999        2007-09-22 00:00:00     Homework #1   20          0           24
2999        2007-09-22 00:00:00     Final Exam    57          0           35

Answer 1

Select
   ID,
   AssnDate,
   AssnTxt,
   Max(IsNull(Sally,0)) AS Sally,
   Max(IsNull(Ted, 0)) As Ted,
   Max(IsNull(Bob, 0)) As Bob
From vwGrades
Group By
  ID,
  AssnDate,
  AssnTxt