Tables in parent child hierarchy

with
tmp_hier1 as
   ((select table_name as child, null as parent from user_tables
    minus
    select distinct table_name as child, null as parent from user_constraints where constraint_type = 'R')
   union
   select distinct table_name as child, (select distinct table_name from user_constraints ac1 where ac1.constraint_name=ac.r_constraint_name) as parent
   from user_constraints ac where constraint_type = 'R'),
tmp_hier2 as
   (select child, parent, LEVEL as lvl
   from tmp_hier1
   START WITH parent is null
   connect by nocycle prior child = parent
   order by lvl, child)
select child, max(lvl)
from tmp_hier2
group by child
order by max(lvl), child;