oracle TIMESTAMP日期相減

select extract(day from inter) * 24 * 60 * 60 +  
       extract(hour from inter) * 60 * 60 + extract(minute from inter) * 60 +  
       extract(second from inter) "seconds"  
  from (select to_timestamp('20100115112233', 'yyyymmddhh24miss') -  
               to_timestamp('20100101123456', 'yyyymmddhh24miss') inter  
          from dual);