SQL中合并多行记录的方法总汇

-- =============================================================================


-- Title: 在SQL中分类合并数据行


-- Author: dobear Mail(MSN): dobear_0922@hotmail.com


-- Environment: Vista + SQL2005


-- Date: 2008-04-22


-- =============================================================================




--1. 创建表，添加测试数据


CREATE TABLE tb(id int, [value] varchar(10))


INSERT tb SELECT 1, 'aa'


UNION ALL SELECT 1, 'bb'


UNION ALL SELECT 2, 'aaa'


UNION ALL SELECT 2, 'bbb'


UNION ALL SELECT 2, 'ccc'




--SELECT * FROM tb




/**//*


id value


----------- ----------


1 aa


1 bb


2 aaa


2 bbb


2 ccc




(5 row(s) affected)


*/






--2 在SQL2000只能用自定义函数实现


----2.1 创建合并函数fn_strSum，根据id合并value值


GO


CREATE FUNCTION dbo.fn_strSum(@id int)


RETURNS varchar(8000)


AS


BEGIN


DECLARE @values varchar(8000)


SET @values = ''


SELECT @values = @values + ',' + value FROM tb WHERE id=@id


RETURN STUFF(@values, 1, 1, '')


END


GO




-- 调用函数


SELECT id, VALUE = dbo.fn_strSum(id) FROM tb GROUP BY id


DROP FUNCTION dbo.fn_strSum




----2.2 创建合并函数fn_strSum2，根据id合并value值


GO


CREATE FUNCTION dbo.fn_strSum2(@id int)


RETURNS varchar(8000)


AS


BEGIN


DECLARE @values varchar(8000)


SELECT @values = isnull(@values + ',', '') + value FROM tb WHERE id=@id


RETURN @values


END


GO




-- 调用函数


SELECT id, VALUE = dbo.fn_strSum2(id) FROM tb GROUP BY id


DROP FUNCTION dbo.fn_strSum2






--3 在SQL2005中的新解法


----3.1 使用OUTER APPLY


SELECT *


FROM (SELECT DISTINCT id FROM tb) A OUTER APPLY(


SELECT [values]= STUFF(REPLACE(REPLACE(


(


SELECT value FROM tb N


WHERE id = A.id


FOR XML AUTO


), '<N value="', ','), '"/>', ''), 1, 1, '')


)N




----3.2 使用XML


SELECT id, [values]=STUFF((SELECT ','+[value] FROM tb t WHERE id=tb.id FOR XML PATH('')), 1, 1, '')


FROM tb


GROUP BY id




--4 删除测试表tb


drop table tb






/**//*


id values


----------- --------------------


1 aa,bb


2 aaa,bbb,ccc




(2 row(s) affected)


*/