Script To Kill Sessions Were Inactive For More Than 15 Minutes

DECLARE
v_sid NUMBER (5);
v_string NUMBER (5);
BEGIN
FOR rec_sec IN (SELECT SID, serial#
FROM v$session
WHERE OSUSER <> 'SYSTEM' AND LAST_CALL_ET > 900)
LOOP
EXECUTE IMMEDIATE ' ALTER SYSTEM KILL SESSION '
|| ''''
|| rec_sec.SID
|| ','
|| rec_sec.serial#
|| ''' IMMEDIATE';
END LOOP;
END;
/