Question

我们说我有一个名为Orders的表，字段为CustomerId，EmployeeId，OrderDate

我想通过最新的OrderDate为每个CustomerId选择所有这些字段。

到目前为止，我已成功选择了CustomerId和OrderDate，但我不知道如何包含EmployeeId

 SELECT [CustomerId], MAX(OrderDate)
      FROM [Orders] 
      GROUP BY [CustomerId]
      ORDER BY [CustomerId]

Answer 1

使用row_number()：

select o.*
from (select o.*,
             row_number() over (partition by customerid order by orderdate desc) as seqnum
      from orders o
     ) o
where seqnum = 1;

这就是＆＃34;传统＆＃34;解。如果您有所有客户的列表，我喜欢使用cross apply：

的解决方案

select o.*
from customers c cross apply
     (select top 1 o.*
      from orders o
      where o.customerid = c.customerid
      order by o.orderdate desc
     ) o;

使用GROUP BY和MAX时如何选择其他表格字段？

1 个答案: