create table master_child as
select k.ptable parent_table,ctable child_table
from (select distinct B.table_name ctable, 
                      a.table_name ptable,
                      b.constraint_name
      from user_constraints A, user_constraints B
      where B.r_constraint_name = A.constraint_name
      and B.r_owner = A.owner
      and B.constraint_type ='R') k, user_cons_columns l
where k.ctable=l.table_name
and k.ptable!=l.table_name
and k.constraint_name = l.constraint_name
order by 1;

select * from master_child order by child_table;

PARENT_TABLE                   CHILD_TABLE                    
------------------------------ ------------------------------ 
REGIONS                        COUNTRIES                      
EMPLOYEES                      DEPARTMENTS                    
LOCATIONS                      DEPARTMENTS                    
DEPARTMENTS                    EMPLOYEES                      
JOBS                           EMPLOYEES                      
DEPARTMENTS                    JOB_HISTORY                    
JOBS                           JOB_HISTORY                    
EMPLOYEES                      JOB_HISTORY                    
COUNTRIES                      LOCATIONS                      

9 rows selected

select parent_table, child_table, level
from master_child
connect by nocycle prior  parent_table = child_tab