create table ta(FieldB varchar(20))
insert into ta 
select 'AAAABBBBBB'
union all select 'CCCCCEEE'
union all select 'CCCCCFFF'
union all select 'DDD'
union all select  'KKKKBDC' 
union all select 'BBBBBB' 
union all select 'MMMDG'
union all select 'GAGAD' 
union all select 'AAAA'
union all select  'EEE'
union all select 'NNNN' 
union all select 'MMM' 
union all select 'FAGFF'
union all select  'CCCCC'

select * from ta

create function F_FieldB()
returns varchar(8000)
as
begin
  declare @str varchar(8000)
  set @str = ''
  select @str = @str + ',' + FieldB from ta 
  set @str = right(@str , len(@str) - 1)
  return(@str)
End

select dbo.F_FieldB()

/*
AAAABBBBBB,CCCCCEEE,CCCCCFFF,DDD,KKKKBDC,BBBBBB,MMMDG,GAGAD,AAAA,EEE,NNNN,MMM,FAGFF,CCCCC
*/

------解决方案--------------------

SQL code
create table tb(fieldB nvarchar(50))
insert into tb select 'AAAA、BBBBBB、CCCCC、EEE'
insert into tb select 'CCCCC、FFF'
insert into tb select 'DDD、KKKKBDC、BBBBBB、MMMDG'
insert into tb select 'GAGAD、AAAA、EEE'
insert into tb select 'NNNN、MMM、FAGFF、CCCCC'
go
select stuff((
select '、'+fieldB from(
select distinct fieldB from(
select substring(a.fieldB,b.number,charindex('、',a.fieldB+'、',b.number+1)-b.number)fieldB 
from tb a,master..spt_values b
where b.type='p' and b.number<=len(a.fieldB) and substring(a.fieldB,b.number,1)<>'、' and substring('、'+a.fieldB,b.number,1)='、'
)t)t1 for xml path('')),1,1,'')
/*
AAAA、BBBBBB、CCCCC、DDD、EEE、FAGFF、FFF、GAGAD、KKKKBDC、MMM、MMMDG、NNNN
*/
go
drop table tb