SQL Statement for Merging Group Columns - Merging Strings by a Certain Field (Simple Merge)

Title: String concatenation by a certain field (simple concatenation)

Description: Merge the value field according to the id field of the following data format.
id　　　 value
----- ------
1　　　　 aa
1　　　　 bb
2　　　　 aaa
2　　　　 bbb
2　　　　 ccc
需要得到结果：
id　　　　 value
------ -----------
1　　　　　 aa,bb
2　　　　　 aaa,bbb,ccc
即：group by id, 求 value 的和（字符串相加）

1、sql2000中只能用自定义的函数解决

create table tb(id int, value varchar(10))
insert into tb values(1, 'aa')
insert into tb values(1, 'bb')
insert into tb values(2, 'aaa')
insert into tb values(2, 'bbb')
insert into tb values(2,'ccc')
go
create function dbo.f_str(@id int) 
returns varchar(100)
as
begin
declare @str varchar(1000) 
set @str='' select @str=@str+''+cast(value as varchar) 
from tb where id = @id 
set @str=right(@str , len(@str) - 1) 
return @str
end
go
--调用函数
select id , value = dbo.f_str(id) from tb group by id
drop function dbo.f_str
drop table tb

2、sql2005中的方法

create table tb(id int, value varchar(10))
insert into tb values(1, 'aa')
insert into tb values(1, 'bb')
insert into tb values(2, 'aaa')
insert into tb values(2, 'bbb')
insert into tb values(2, 'ccc')
go
select id, [value] = stuff((select ',' + [value] from tb t where id = tb.id 
for xml path('')) , 1 , 1 , '')from tb group by id
drop table tb

3、使用游标合并数据

create table tb(id int, value varchar(10))
insert into tb values(1, 'aa')
insert into tb values(1, 'bb')
insert into tb values(2, 'aaa')
insert into tb values(2, 'bbb')
insert into tb values(2, 'ccc')
go
declare @t table(id int,value varchar(100))
--Define result set table variable
--Define cursor and perform merge processing
declare my_cursor cursor local for
select id , value from tb
declare @id_old int , @id int , @value varchar(10) , @s varchar(100)
open my_cursor fetch my_cursor into @id , @value
select @id_old = @id , @s=''while @@FETCH_STATUS = 0
begin
 if @id = @id_old
  select @s = @s + ',' + cast(@value as varchar) else
  begin
  insert @t values(@id_old , stuff(@s,1,1'')) 
  select @s = ',' + cast(@value as varchar) , @id_old = @id
  end
 fetch my_cursor into @id , @value END 
 insert @t values(@id_old , stuff(@s,1,1''))
 close my_cursor
 deallocate my_cursor
 select * from @t
drop table tb

That is the introduction to the SQL statement for merging grouped characters. I hope it is helpful to everyone.