Oracle 字符型时间相减取小时

  select Round(To_Number(To_Date(replace(substr('2010-05-01 02:44:17', -8),':',''), 'HH24MISS') -
                         To_Date(replace(substr('2010-05-01 00:07:00', -8),':',''),
                                 'HH24MISS')) * 24, 1) 小时
    From Dual;