spin thru family table starting at parent_key is null

ch7_2.sql

WITH RSFC(CK,PK,LVL) AS
  ( SELECT CHILD_KEY,PARENT_KEY,0 AS LVL FROM FAMILY WHERE PARENT_KEY IS NULL
  UNION ALL
  SELECT CHILD_KEY,
    PARENT_KEY,
    LVL+1
  FROM RSFC R
  INNER JOIN FAMILY F
  ON R.CK = F.PARENT_KEY
  )
SELECT * FROM RSFC