with tmp_tbl as
 (select 10 old_id, 20 as new_id from dual
  union
  select 20 old_id, 30 as new_id from dual
  union
  select 30 old_id, 40 as new_id from dual
  union
  select 50 old_id, 60 as new_id from dual
  union
  select 60 old_id, 70 as new_id from dual
)
select * from tmp_tbl;

    OLD_ID     NEW_ID
---------- ----------
        10         20
        20         30
        30         40
        50         60
        60         70

    OLD_ID     NEW_ID
---------- ----------
        10         40
        20         40
        30         40
        50         70
        60         70

with tmp_tbl as
 (select 10 old_id, 20 as new_id from dual
  union
  select 20 old_id, 30 as new_id from dual
  union
  select 30 old_id, 40 as new_id from dual
  union
  select 50 old_id, 60 as new_id from dual
  union
  select 60 old_id, 70 as new_id from dual
),
final_tbl (old_id, new_id, high_level) as
(select a.old_id, b.new_id, 1
   from tmp_tbl a, tmp_tbl b
  where a.new_id = b.old_id
 union all
 select a.old_id, b.new_id, high_level+1
   from tmp_tbl a, final_tbl b
  where a.old_id = b.old_id
)
cycle old_id set cyc to '1' default '0' 
select * from final_tbl;

    OLD_ID     NEW_ID HIGH_LEVEL CYC
---------- ---------- ---------- ---
        10         30          1 0
        20         40          1 0
        50         70          1 0
        10         30          2 1
        20         40          2 1
        50         70          2 1

SQL> with tmp_tbl as
  2   (select 10 old_id, 20 as new_id from dual
  3    union
  4    select 20 old_id, 30 as new_id from dual
  5    union
  6    select 30 old_id, 40 as new_id from dual
  7    union
  8    select 50 old_id, 60 as new_id from dual
  9    union
 10    select 60 old_id, 70 as new_id from dual
 11  )
 12  select connect_by_root old_id old_id, new_id
 13  from tmp_tbl
 14  where connect_by_isleaf = 1
 15  connect by prior new_id = old_id
 16  /
    OLD_ID     NEW_ID
---------- ----------
        10         40
        20         40
        30         40
        50         70
        60         70