SET NOCOUNT ON
DECLARE @T TABLE (a VARCHAR(10),b INT)
----------- 
INSERT @T SELECT 'str1'  ,1 
INSERT @T SELECT 'str1'  ,1 
INSERT @T SELECT 'str1'  ,1 
INSERT @T SELECT 'str2'  ,1 
INSERT @T SELECT 'str2'  ,1 
INSERT @T SELECT 'str2'  ,1 
INSERT @T SELECT 'str2'  ,1 
INSERT @T SELECT 'str2'  ,1 
INSERT @T SELECT 'str3' , 1 
INSERT @T SELECT 'str3',  1
SELECT A,B=ROW_NUMBER() OVER(PARTITION BY A ORDER BY GETDATE()) FROM @T
/**A          B
---------- --------------------
str1       1
str1       2
str1       3
str2       1
str2       2
str2       3
str2       4
str2       5
str3       1
str3       2
/

------解决方案--------------------
SQL code
select a,b=row_number() over(partition by a order by a)
from tb