--> 测试数据：[tb]
IF OBJECT_ID('[tb]') IS NOT NULL DROP TABLE [tb]
GO 
CREATE TABLE [tb]([id] INT,[name] VARCHAR(7))
INSERT [tb]
SELECT 1,'AA333AB' UNION ALL
SELECT 2,'AA555AB' UNION ALL
SELECT 3,'BB666AC' UNION ALL
SELECT 4,'BB555AC' UNION ALL
SELECT 5,'CC777'
--------------开始查询--------------------------

SELECT * FROM [tb] AS t
WHERE NOT EXISTS (SELECT 1 FROM tb WHERE SUBSTRING([name],3,3)=SUBSTRING(t.[name],3,3) AND id<t.id )

----------------结果----------------------------
/* 
id          name
----------- -------
1           AA333AB
2           AA555AB
3           BB666AC
5           CC777

(4 行受影响)


*/

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

select
 * 
from
 tb t 
where
 id=(select min(id) from tb where substring(name,3,3)=substring(t.name,3,3))

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

DECLARE @TABLE1 TABLE([ID] INT,[NAME] VARCHAR(7))
INSERT @TABLE1
SELECT 1,'AA333AB' UNION ALL
SELECT 2,'AA555AB' UNION ALL
SELECT 3,'BB666AC' UNION ALL
SELECT 4,'BB555AC' UNION ALL
SELECT 5,'CC777'

SELECT * FROM @TABLE1 T
WHERE ID=(SELECT MIN(ID) FROM @TABLE1 WHERE SUBSTRING(NAME,3,3)=SUBSTRING(T.NAME,3,3))
/*
ID          NAME
----------- -------
1           AA333AB
2           AA555AB
3           BB666AC
5           CC777
*/