does it help?

SET NOCOUNT ON;

DECLARE @t TABLE (st_no INT, year INT, month INT, sal MONEY)

INSERT INTO @t (st_no, year, month, sal) SELECT 1,2008,1,1000

INSERT INTO @t (st_no, year, month, sal) SELECT 1,2008,2,1000

INSERT INTO @t (st_no, year, month, sal) SELECT 1,2008,3,1000

INSERT INTO @t (st_no, year, month, sal) SELECT 1,2008,4,1010

INSERT INTO @t (st_no, year, month, sal) SELECT 1,2008,5,1010

INSERT INTO @t (st_no, year, month, sal) SELECT 1,2008,6,1010

INSERT INTO @t (st_no, year, month, sal) SELECT 1,2008,7,1010

INSERT INTO @t (st_no, year, month, sal) SELECT 1,2008,8,1020

;WITH cte AS (

SELECT *,

ROW_NUMBER() OVER(PARTITION BY sal ORDER BY year, month, sal) AS seq

FROM @t

)

SELECT year, month, sal, seq

FROM cte

WHERE seq = 1

/*

year month sal seq

----------- ----------- --------------------- --------------------

2008 1 1000.00 1

2008 4 1010.00 1

2008 8 1020.00 1

*/