Sql server 选择键相同但某个属性最低的行

我有下表

Key    Year_month    Ammount  
1      201612        100  
1      201701        120
2      201605        1000
2      201608        800
3      201705        500

我只需要使用最低的年/月值为每个键选择一行

e、 g:这应该是查询的结果

Key    Year_month    Ammount  
1      201612        100  
2      201605        1000
3      201705        500

问题是我真的不知道该怎么做，我试着用

SELECT   
      KEY,
      YEAR_MONTH,  
      AMMOUNT
FROM TABLE AS T1
WHERE YEAR_MONTH =(SELECT TOP 1 YEAR_MONTH FROM TABLE WHERE KEY = T1.KEY)

但这不起作用

另一种方法

declare @table table ([key] int, year_month int, amount int)

insert into @table ([key], year_month, amount)
values (1, 201612, 100),  
       (1, 201701, 120),
       (2, 201605, 1000),
       (2, 201608, 800),
       (3, 201705, 500)


select t.*,
       (select t2.amount from @table t2 where t2.[key] = t.[key] and t2.year_month = t.year_month) as amount
from   ( select [key], min(year_month) as year_month
         from   @table 
         group by [key]
       ) t

这是回报

key year_month  amount  
--- ----------  ------  
1   201612      100 
2   201605      1000    
3   201705      500 

试试这个

DECLARE @T TABLE
(
    [Key] INT,
    Year_month VARCHAR(10),
    Amount FLOAT
)

INSERT INTO @T
VALUES('1','201612','100'),
('1','201701','120'),
('2','201605','1000'),
('2','201608','800'),
('3','201705','500')

;WITH CTE
AS
(
    SELECT
        RN = ROW_NUMBER() OVER(PARTITION BY [Key] ORDER BY CAST(Year_month+'01' AS DATE) ASC),
        *
        FROM @T
)
SELECT
    [Key],
    Year_month,
    Amount
    FROM CTE
        WHERE RN = 1

Select DT.* FROM Data_Table DT
    JOIN
       ( SELECT [KEY], Min(Year_month) AS MinYM FROM Data_Table GROUP BY [KEY] ) DX
        ON DX.[KEY]= DT.[KEY] AND DX.MinYM = DT.Year_month ;

DROP TABLE IF EXISTS #tmp_test01

CREATE TABLE #tmp_test01 ( [KEY]        INT
                         , Year_Month   INT
                         , Amount       INT
                         )

INSERT INTO #tmp_test01 
VALUES 
  (1, 201612, 100)  
, (1, 201701, 120)
, (2, 201605, 1000)
, (2, 201608, 800)
, (3, 201705, 500)


WITH CTE AS (

SELECT ROW_NUMBER() OVER (PARTITION BY [KEY]  ORDER BY [KEY], [Year_Month]) RN
     , [KEY]
     , Year_Month
     , Amount
FROM #tmp_test01

)

SELECT [KEY]
     , Year_Month
     , Amount
FROM CTE
WHERE RN = 1