Top events online

select * from (
select t1.*, rownum rn from
(
SELECT event, time_waited,
round(time_waited*100/ SUM (time_waited) OVER(),2) wait_pct
FROM (SELECT event, time_waited
FROM v$session_event
WHERE event NOT IN
('Null event',
'client message',
'rdbms ipc reply',
'smon timer',
'rdbms ipc message',
'PX Idle Wait',
'PL/SQL lock timer',
'file open',
'pmon timer',
'WMON goes to sleep',
'virtual circuit status',
'dispatcher timer',
'SQL*Net message from client',
'parallel query dequeue wait',
'pipe get'
) UNION
(SELECT NAME, VALUE
FROM v$sysstat
WHERE NAME LIKE 'CPU used when call started'))
ORDER BY 2 desc) t1)
where rn <= 20;