declare @T table (col1 int,col2 varchar(1),col3 varchar(1),col4 varchar(1))
insert into @T
select 123,'a','b','c' union all
select 123,'a','b','d' union all
select 123,'a','b','c' union all
select 456,'e','f','h' union all
select 456,'e','f','h'

select TOP 2 * from @T
/*
col1        col2 col3 col4
----------- ---- ---- ----
123         a    b    c
123         a    b    d
*/

------解决方案--------------------
SQL code

WITH CTE AS(
SELECT *,ROW_NUMBER() OVER(PARTITION BY 行号,字段1,字段2,字段3) AS RN
FROM 表
)
SELECT * FROM CTE WHERE RN = 1