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)
*/