for drop user username cascade
In some case, we may want to drop user.
so we can use this sql as follow:
drop user username cascade;
but if the user is connected, we can't drop it.
so first , we should find which one is connected
we can use
select username,sid, serial# from v$session
then
alter system kill session 'sid,serial';
here may pay attention, there may be many connections, so nee kill more than one time.
drop user 'yourname' cascade;