Declare @ID int, @Dept varchar(max)
Set @ID = 3;

With DeptHier(ID, ParentID)
as
(
	Select ID, ParentID
	From Dept
	Where ID = @ID

	union all

	Select Dept.ID, Dept.ParentID
	From Dept JOIN DeptHier
	On Dept.ID = DeptHier.ParentID
)
Select @dept = Coalesce(@dept + '/', '') + d.Name 
from Dept d Join DeptHier dh 
on d.ID = dh.ID
order by dh.ParentID

select @dept as Dept