SQL 合并多行记录的方法总汇

SQL中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

--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
), '', ''), 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