Question

我目前有多条记录，但我只需要一条记录。我曾尝试过Cross申请，但似乎我缺少了一些我自己无法ping的东西。相反，我得到了一个完全不同的值，即使在提供的表中的记录中也没有。

任何帮助将不胜感激。

id         subject          enrollmentdate    roomNum  
00045       science         3-3-2016             98
00045       science         3-3-2016             52
00089       math            7-25-2017            13
00089       math            7-25-2017            56
00123       social studies  3-1-2016             02
00136       gym             5-2-2017             01
00159       math            9-2-2017             96

查询：

select  d.id, c.subject, c.Enrollmentdate, ds.roomNum
from  #classrooms as c 
 cross apply 
     (select top 1 roomNum, subject,Enrollmentdate
      from  #classrooms 
      where subject = c.subject
      and enrollmentdate = c.enrollmentdate
      order by id desc) as ds

结果：

 id         subject          enrollmentdate    roomNum  
    00045       science         3-3-2016             66
    00045       science         3-3-2016             66

Answer 1

如果您只需要一个（而不在乎哪个），那么类似的方法可能会有所帮助：

select id, 
       subject, 
       enrollmentdate, 
       max(roomnum) max_roomnum
from #classrooms
group by id, 
         subject, 
         enrollmentdate;

Answer 2

如果您要特定的商品，可以使用top with ties：

select top (1) with ties c.*
from #classrooms c
order by row_number() over (partition by id, subject, enrollmentdate order by roomNum desc);

或者是真正随机的一个：

select top (1) with ties c.*
from #classrooms c
order by row_number() over (partition by id, subject, enrollmentdate order by newid() desc);

选择最上面的重复记录

2 个答案: