合并列值整理

数据：
id col
----- ------
1 a
1 b
2 a
2 b
2 c

期望得到结果：
id col
------ -----------
1 a,b
2 a,b,c

----------------------------------------------------------------------------------
-- Author : htl258(Tony)
-- Date : 2009-03-15 10:19:22
-- Version: Microsoft SQL Server 2008 (RTM) - 10.0.1600.22 (Intel X86)
-- Jul 9 2008 14:43:34
-- Copyright (c) 1988-2008 Microsoft Corporation
-- Developer Edition on Windows NT 5.1 <X86> (Build 2600: Service Pack 2)
-- Blog : http://blog.csdn.net/htl258 ----------------------------------------------------------------------------------
--> 生成测试数据表: [tb]
IF OBJECT_ID('[tb]') IS NOT NULL
DROP TABLE [tb]
GO
CREATE TABLE [tb] ([id] [int],[col] [nvarchar](10))
INSERT INTO [tb]
SELECT '1','a' UNION ALL
SELECT '1','b' UNION ALL
SELECT '2','a' UNION ALL
SELECT '2','b' UNION ALL
SELECT '2','c'

--SELECT * FROM [tb]

-->SQL查询如下:
--SQL2000以上版本:
IF OBJECT_ID('dbo.f_str')>0
DROP FUNCTION dbo.f_str
GO
CREATE FUNCTION dbo.f_str
(
@id INT
)
RETURNS VARCHAR(1000)
AS
BEGIN
DECLARE @r VARCHAR(1000)
SELECT @r = ISNULL(@r+',', '') + col
FROM tb
WHERE id = @id
RETURN @r
END
GO
SELECT DISTINCT id,dbo.f_str(id) col FROM tb
/*
id col
----------- ---------------------
1 a,b
2 a,b,c

(2 行受影响)
*/

-->SQL2005以上版本：
SELECT DISTINCT id,
STUFF(
(
SELECT ','+col
FROM tb t
WHERE id = tb.id FOR XML PATH('')
), 1, 1, ''
) AS col
FROM tb
/*
id col
----------- ---------------------
1 a,b
2 a,b,c

(2 行受影响)
*/