如果非得要查 30 天，那也有办法：

alter session set nls_date_format='yyyy-mm-dd hh24:mi';
alter session set nls_timestamp_format='yyyy-mm-dd hh24:mi';
column dbtime format 999,999,999
SET ECHO OFF
SET TERMOUT OFF
SET TRIMOUT OFF
set feedback off
set heading on
set linesize 400
set pagesize 10000
select c.instance_number,
c.begin_interval_time,
nvl(((select max(b.value)
from DBA_HIST_SYS_TIME_MODEL b
where b.snap_id = a.snap_id + 1
and b.stat_name = a.stat_name
and b.instance_number = a.instance_number
and b.dbid=a.dbid)
-(select max(b.value)
from DBA_HIST_SYS_TIME_MODEL b
where b.snap_id = a.snap_id
and b.stat_name = a.stat_name
and b.instance_number = a.instance_number 
and b.dbid=a.dbid)),0)/100000/60 dbtime
from DBA_HIST_SYS_TIME_MODEL a, sys.WRM$_SNAPSHOT c
where a.stat_name = 'DB time'
and a.instance_number = c.instance_number
and a.snap_id = c.snap_id
and c.begin_interval_time >
GREATEST((select max(STARTUP_TIME) from v$instance), sysdate - 30)
order by 1,2;

把以上查询结果导入到 excel 中，然后生成折线图，我们以前就这么干过。要是查到了 30 天 ，你看看曲线图长啥样。