Sql 选择顶部重复记录

我目前有多条记录，但我只需要一条记录。我尝试过交叉应用，但似乎我错过了一些我自己似乎无法理解的东西。相反，我得到了一个完全不同的值，它甚至不在提供的表中的记录中

任何帮助都将不胜感激

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

如果您只需要一个（并且不太关心哪一个），那么下面的内容可能会有所帮助：

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

如果您只需要一个（并且不太关心哪一个），那么下面的内容可能会有所帮助：

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

---

如果您想要一个特定的，您可以使用带领带的

top

：

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

或者对于一个真正随机的：

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

---

如果您想要一个特定的，您可以使用带领带的

top

：

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

或者对于一个真正随机的：

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

---

您想选择哪一条记录？我们可以根据什么规则找到它？分组类似的行似乎是您所需要的。你能举一个你想分组的行的例子吗？在“相似”比较中，您将包括哪些列？您希望选择哪一条记录？我们可以根据什么规则找到它？分组相似的行似乎是您所需要的。你能举一个你想分组的行的例子吗？在“相似”比较中，您会包括哪些列？