--unlock table 
select t2.username, t2.sid, t2.serial#, t2.logon_time
from v$locked_object t1, v$session t2
where t1.session_id=t2.sid order by t2.logon_time;
alter system kill session 'sid,serial#';

--delete a connected user forcibly
select sid, serial# from v$session where user='USERNAME';
alter system kill session 'sid,serial#';
drop user username cascade;