----------------------------
-- Author  :fredrickhu(小F，向高手学习)
-- Date    :2011-04-01 14:01:35
-- Verstion:
--      Microsoft SQL Server 2008 (RTM) - 10.0.1600.22 (Intel X86) 
--    Jul  9 2008 14:43:34 
--    Copyright (c) 1988-2008 Microsoft Corporation
--    Enterprise Edition on Windows NT 5.2 <X86> (Build 3790: Service Pack 2)
--
----------------------------
--> 测试数据：[tb]
if object_id('[tb]') is not null drop table [tb]
go 
create table [tb]([col1] text,[col2] text)
insert [tb]
select 'a','t' union all
select 'a','t' union all
select 'a','t'
--------------开始查询--------------------------
select distinct (CAST (col1 as varchar(10))),(CAST (col2 as varchar(10))) from tb
----------------结果----------------------------
/*            
---------- ----------
a          t

(1 行受影响)

*/