declare @dna varchar(20), @temp varchar(20)
select @dna=''
declare dna_cur cursor for select dna from D_Area
open  dna_cur
  fetch next from dna_cur into @temp
  while @@fetch_status=0
    begin
      if @temp is not null
         begin
           select @dna=@dna + ',' + isnull(@temp,'')
         end
      fetch next from dna_cur into @temp
    end
close dna_cur
deallocate dna_cur
select @dna=substring(@dna,2,len(@dna)-1)
print @dna

declare @dna varchar(20)
select @dna=''
select @dna=@dna + isnull(dna,'') + ',' from D_Area --where dna is not null
if @dna is null
   begin
     print 'null'
   end
else
   begin
     print @dna
   end