KILL SESSION

Kill all session for given sqlid :

select 'alter system kill session ' ||''''||SID||','||SERIAL#||' immediate ;' from v$session 
where sql_id='&sql_id'; 

Kill all session for given sqlid (RAC) 

select 'alter system kill session ' ||''''||SID||','||SERIAL#||',@'||inst_id||''''||' immediate ;' 
from gv$session where sql_id='&sql_id';

Kill all session for given user (RAC)

select 'alter system kill session ' ||''''||SID||','||SERIAL#||',@'||inst_id||''''||' immediate ;' 
from gv$session where username='&username';