--測試資料
CREATE TABLE tb(
ID1 char(2) NOT NULL,
ID2 char(4) NOT NULL,
col int,
PRIMARY KEY(ID1,ID2))
INSERT tb SELECT 'aa','0001',1
UNION ALL SELECT 'aa','0003',2
UNION ALL SELECT 'aa','0004',3
UNION ALL SELECT 'bb','0005',4
UNION ALL SELECT 'bb','0006',5
UNION ALL SELECT 'cc','0007',6
UNION ALL SELECT 'cc','0009',7
GO

--重排編號處理
DECLARE @ID1 char(2),@ID2 int
UPDATE a SET ID2=RIGHT(10000
	+(SELECT COUNT(*) FROM tb WHERE ID1=a.ID1 AND ID2<=a.ID2)
	,4)
FROM tb a
SELECT * FROM tb
/*--結果
ID1  ID2  col
---- ---- ----------- 
aa   0001 1
aa   0002 2
aa   0003 3
bb   0001 4
bb   0002 5
cc   0001 6
cc   0002 7
--*/