select ('1,2,3,4') as AA,1 id from DUAL
  union all
  select ('4,5,6,7') as AA,2 id from DUAL
  union all
  select ('7,8,9') as aa,3 id from dual

  with TEMP as(
  select ('1,2,3,4') as AA,1 id from DUAL
  union all
  select ('4,5,6,7') as AA,2 id from DUAL
  union all
  select ('7,8,9') as aa,3 id from dual
  )
  select REGEXP_SUBSTR(aa, '[^,]+', 1, level) as bb,  id
           from temp
          where  aa is not null
                    connect by level <= REGEXP_COUNT(AA, '[^,]+')
                    and id= prior id
                   and prior DBMS_RANDOM.value > 0;