set nocount on
declare @level int
set @level = 1

create table #tree (id int identity (1,1), dataid int, level int)

insert #tree (dataid, level)
	select dataid, @level
	from dirtable where parentid = 0 -- or is null

While @@rowcount > 0
begin
	set @level = @level + 1
	insert #tree (dataid, level)
		select d.dataid, @level 
		from dirtable d
		inner join #tree t on t.dataid = d.parentid
		where t.level = @level - 1
		order by dirname
end

Select dirname from #tree t
inner join dirtable d on t.id = t.dataid
order by id

drop table #tree