SQL Server CTE -Find top parentID forEach childID?

Question

I have a table which contains hierarchy data - something like:

childID  |  parentID
____________________
  1      |     5
  5      |     9
  9      |     20         


        

Answer 1

select distinct 
       a.ChildID,a.ParentID,
       --isnull(nullif(c.parentID,b.parentID),a.parentID) as toppa,
       B.parentID
       --,c.parentID
      ,isnull(nullif(d.parentID,a.parentID),c.parentID) as toppa1,a.name
from myTable a
   inner join myTable c
       on a.parentID=c.parentID
   inner join myTable b
       on b.childID=a.parentID
   inner join myTable d
       on d.childID=b.parentID