提供字符串的替代聚合函数

--test_id test_value
--------------------
'a' '01,03,04,02'
'b' '03,04,08,06,09'
'c' '09,10'

--代码-------------------------------------------GO
GO
if object_id(N'dbo.merge',N'FN') is not null
drop function dbo.merge
GO
--函数功能:字符串聚合及去除重复值
create function dbo.merge
(
@test_id varchar(50)
)
returns varchar(50)
as
begin
--字符串聚合-------------------------START
declare @s varchar(8000)
set @s = ''

select
@s = @s + test_value + ','
from test_a
where test_id = @test_id
--字符串聚合-------------------------END

--去除重复值-------------------------START
declare @value varchar(8000)--存储第一个逗号前的值
declare @result varchar(8000)--存储唯一值的中间字符串
set @result = ''

--有值的场合
while charindex(',',@s) <> 0
begin
--取第一个逗号前的值
set @value = left(@s,charindex(',',@s) -1)

--第一个逗号前的值没在结果中出现
if charindex(',' + @value + ',',',' + @result) = 0
begin
--加入中间字符串
set @result = @result + @value + ','
end

--去除第一个值以及后面的逗号(剔除法),继续循环判断
set @s = right(@s,(len(@s) - charindex(',',@s)))
end

set @s = @result
--去除重复值-------------------------END

return left(@s,len(@s)-1)
end
GO

if object_id(N'test_a',N'U') is not null
drop table test_a
GO

create table test_a
(
test_id varchar(50),
test_value varchar(50)
)

insert into test_a
select 'a','01,03,04' union all
select 'a','02,04' union all
select 'b','03,04,08' union all
select 'b','06,08,09' union all
select 'c','09' union all
select 'c','10'

select
test_id,
test_value = dbo.merge(test_id)
from test_a
group by test_id