1,10
1,11
1,12
2,10
2,13

10,aaa,1
11,bbb,2
12,ccc,3
13,ddd,4

aid,bname,bprice

1,aaa,1
,bbb,2
,ccc,3
2,aaa,1
,ddd,4

CREATE TABLE #T1(aid int ,bid int)
INSERT INTO #T1
SELECT 1,10 UNION ALL
SELECT 1,11 UNION ALL
SELECT 1,12 UNION ALL
SELECT 2,10 UNION ALL
SELECT 2,13
CREATE TABLE #T2(bid int,bname nvarchar(10),bprice int)
INSERT INTO #T2
SELECT 10,''aaa'',1 UNION ALL
SELECT 11,''bbb'',2 UNION ALL
SELECT 12,''ccc'',3 UNION ALL
SELECT 13,''ddd'',4
SELECT A.aid,B.bname,B.bprice INTO #T3 FROM #T1 
AS A LEFT OUTER JOIN #T2 AS B ON A.bid=B.bid
DECLARE @aid int ,@lastaid int

UPDATE #T3 SET @aid=(CASE WHEN ISNULL(@lastaid,'''') 
=aid THEN NULL ELSE aid END),aid=@aid,@lastaid=aid
SELECT * FROM #T3
DROP TABLE #T1,#T2,#T3

/*
1 aaa 1
NULL bbb 2
NULL ccc 3
2 aaa 1
NULL ddd 4
*/