How to check the uptime of a database

Query:
=====

col STIME for a30
col HOST_NAME for a20
col UPTIME for a40
set lines 300
set pages 200
select
    host_name
   , instance_name
   ,status
   , to_char(startup_time,'DD-MON-YYYY HH24:MI:SS') stime
   , floor(sysdate - startup_time) || ' days ' ||
   trunc( 24*((sysdate-startup_time) -
   trunc(sysdate-startup_time))) || ' hour ' ||
   mod(trunc(1440*((sysdate-startup_time) -
   trunc(sysdate-startup_time))), 60) ||' minute ' ||
   mod(trunc(86400*((sysdate-startup_time) -
   trunc(sysdate-startup_time))), 60) ||' seconds' uptime
from

sys.gv_$instance;

OutPut:

======

HOST_NAME        INSTANCE_NAME    STATUS       STIME                          UPTIME

--------------- ---------------- ------------ ------------------------------ --------------------

testpdb01          TEST1           OPEN         20-NOV-2015 21:32:56           12 days 6 hour 52 minute