SELECT 
   EXTRACT(DAY FROM (sysdate-to_date('2012-03-29 00:00:00','YYYY-MM-DD HH24:MI:ss')) DAY TO SECOND )
   || ' days '
   || EXTRACT(HOUR FROM (sysdate-to_date('2012-03-29 00:00:00','YYYY-MM-DD HH24:MI:ss')) DAY TO SECOND )
   || ' hours'
   || EXTRACT(MINUTE FROM (sysdate-to_date('2012-03-29 00:00:00','YYYY-MM-DD HH24:MI:ss')) DAY TO SECOND )
   || ' minute'
   || EXTRACT(SECOND FROM (sysdate-to_date('2012-03-29 00:00:00','YYYY-MM-DD HH24:MI:ss')) DAY TO SECOND )
   || ' second' "Interval"
FROM DUAL;

------解决方案--------------------
SQL code


select trunc(t/86400) 天,
       trunc((mod(t,86400))/3600) 时,
       trunc(mod(mod(t,86400),3600)/60) 分, 
       mod(mod(mod(t,86400),3600),60) 秒
from
(select (sysdate-to_date('2012-03-20 12:12:12','yyyy-mm-dd hh24:mi:ss'))*86400 t from dual)

    天    时    分    秒
-------------------------------------------
1    9    21    50    10

------解决方案--------------------
或者调用存储过程

SQL code

CREATE OR REPLACE Function timeinterval (d_begindate Date,d_enddate Date) --计算两个日期之间相差的天数、小时数、分钟数、秒数
Return Varchar2
Is
s_timeinterval Varchar2(40);n_timeinterval Number;n_day Number;n_hour Number;n_minute Number;n_second Number;n_timesurplus Number;
Begin
  If d_begindate Is Null Or d_enddate Is Null Then
     s_timeinterval:=Null;
  Else
    Select (d_enddate-d_begindate)*24*60*60 Into n_timeinterval From dual;
    n_day:=floor(n_timeinterval/24/60/60);
    n_timesurplus:=Mod(n_timeinterval,24*60*60);
    n_hour:=floor(n_timesurplus/60/60);
    n_timesurplus:=Mod(n_timesurplus,60*60);
    n_minute:=floor(n_timesurplus/60);
    n_timesurplus:=Mod(n_timesurplus,60);
    n_second:=floor(n_timesurplus);
    s_timeinterval:=n_day||'天'||n_hour||'小时'||n_minute||'分'||n_second||'秒';
  End If;
  Return s_timeinterval;
End;