SQL查询
有以下数据：

id type level price
1 m_p1 1 50
2 m_p2 1 50
3 m_p3 2 30
4 m_p3 2 30


查询level的值（1，2）各自对应一条数据

要得到以下结果

id type level price
1 m_p1 1 50
3 m_p3 2 30
[解决办法]

----------------------------
-- Author  :DBA_Huangzj()
-- Date    :2013-02-21 17:55:32
-- Version:
--      Microsoft SQL Server 2008 R2 (SP1) - 10.50.2500.0 (X64) 
--Jun 17 2011 00:54:03 
--Copyright (c) Microsoft Corporation
--Enterprise Edition (64-bit) on Windows NT 6.1 <X64> (Build 7601: Service Pack 1, v.721)
--
----------------------------
--> 测试数据：[huang]
if object_id('[huang]') is not null drop table [huang]
go 
create table [huang]([id] int,[type] varchar(4),[level] int,[price] int)
insert [huang]
select 1,'m_p1',1,50 union all
select 2,'m_p2',1,50 union all
select 3,'m_p3',2,30 union all
select 4,'m_p3',2,30
--------------开始查询--------------------------
SELECT  *
FROM    ( SELECT    * ,
                    ROW_NUMBER() OVER ( PARTITION BY [level] ORDER BY id ) pid
          FROM      [huang] a
          WHERE     [level] IN ( 1, 2 )
        ) a
WHERE   pid = 1

----------------结果----------------------------
/* 
id          type level       price       pid
----------- ---- ----------- ----------- --------------------
1           m_p1 1           50          1
3           m_p3 2           30          1

(2 行受影响)
*/

[解决办法]
select * from tb where id in (select min(id) from tb group by level)