sql-server-2008 - 如何通过使用group by命令从检索到的结果中获取每个组的第一条记录

Question

假设我的输入是：

ID  GroupID  Qty
1         1  100
2         1  200
3         1  300
4         2  98
5         2  198
6         3  175
7         3  275
8         3  375
9         4  215

输出应为

ID   GroupID    Qty
 1         1    100
 4         2    98
 6         3    175
 9         4    215

谁能帮我如何使用SQL Server T-SQL查询做到这一点？

Answer 1

declare @T table (ID int, GroupID int, Qty int)
insert into @T values
(1, 1, 100),
(2, 1, 200),
(3, 1, 300),
(4, 2, 98),
(5, 2, 198),
(6, 3, 175),
(7, 3, 275),
(8, 3, 375),
(9, 4, 215)

;with cte as
(
  select
    ID,
    GroupID,
    Qty,
    rank() over(partition by GroupID order by ID) as rn
  from @T
)  
select ID, GroupID, Qty
from cte
where rn = 1