Question

我希望我能解释我所拥有的问题，并希望能够指出我的方向。

我试图通过（电子邮件地址）对数据子集进行分组，然后我在日期字段上使用max()，但由于其他字段中的值不同，带回更多行然后需要。

我只想返回每个电子邮件地址的最大记录，并返回最大记录中同一行的字段。

不确定我怎么能写这个查询？

Answer 1

这是ROW_NUMBER的任务：

select *
from
 ( 
   select t.*,
      -- assign sequential number starting with 1 for the maximum date 
      row_number() over (partiton by email_address order by datecol desc) as rn
   from tab
 ) as dt
where rn = 1 -- only return the latest row

Answer 2

您可以使用row_number()编写此查询：

select t.*
from (select t.*,
             row_number() over (partition by emailaddress order by date desc) as seqnum
      from t
     ) t
where seqnum = 1;

Answer 3

这样的事情怎么样？

select a.*
from baseTable as a
inner join
(select Email,
       Max(EmailDate) as EmailDate
from baseTable
group by Email) as b
on a.Email = b.Email
and a.EmailDate = b.EmailDate

SQL Server Group By with Max on Date字段

3 个答案: