SELECT * FROM ...

alter system kill session...

SCOTT@orcl_11gR2> select * from emp where deptno = 10 for update;

     EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM
---------- ---------- --------- ---------- --------- ---------- ----------
    DEPTNO
----------
      7782 CLARK      MANAGER         7839 09-JUN-81       2450
        10

      7839 KING       PRESIDENT            17-NOV-81       5000
        10

      7934 MILLER     CLERK           7782 23-JAN-82       1300
        10


3 rows selected.

SCOTT@orcl_11gR2>

SCOTT@orcl_11gR2> truncate table emp;
truncate table emp
               *
ERROR at line 1:
ORA-00054: resource busy and acquire with NOWAIT specified or timeout expired


SCOTT@orcl_11gR2> select s.sid, s.serial#
  2  from   all_objects ao, v$locked_object lo, v$session s
  3  where  ao.object_name = 'EMP'
  4  and    ao.object_id = lo.object_id
  5  and    lo.session_id = s.sid;

       SID    SERIAL#
---------- ----------
       133        724

1 row selected.

SCOTT@orcl_11gR2> alter system kill session '133,724';

System altered.

SCOTT@orcl_11gR2> truncate table emp;

Table truncated.

SCOTT@orcl_11gR2>