SQL 合并多行记录的方法总汇

–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/SQL2008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)
*/