学习一个sql语句，检查数据库启动的时间：
SQL> select to_char(startup_time,'DD-MON-YYYY HH24:MI:SS') started_at,
TRUNC(sysdate - (startup_time))||'day(s),'||TRUNC(24*((sysdate-startup_time) -TRUNC(sysdate-startup_time)))
||'hour(s),'||MOD(TRUNC(1440*((SYSDATE-startup_time)-
TRUNC(sysdate-startup_time))),60)
||'minutes(s),'||MOD(TRUNC(86400*((SYSDATE-STARTUP_TIME)-
TRUNC(SYSDATE-startup_time))),60)
||'seconds' uptime
from v$instance;
STARTED_AT
-----------------------
UPTIME
--------------------------------------------------------------------------------
02-NOV-2009 16:00:31
62day(s),18hour(s),45minutes(s),0seconds
SQL>