捕获锁表异常

/* Formatted on 2011/01/07 09:07 (Formatter Plus v4.8.8) */
DECLARE
   e_failed_to_lock   EXCEPTION;
   PRAGMA EXCEPTION_INIT (e_failed_to_lock, -54);
   v_tax_rate             NUMBER;
BEGIN
   SELECT     tax_rate
         INTO v_tax_rate
         FROM gl_tax_branch
        WHERE tax_type = 'WT3' AND branch = '802101'
   FOR UPDATE NOWAIT;
EXCEPTION
   WHEN e_failed_to_lock
   THEN
      DBMS_OUTPUT.put_line ('............locked!');
END;
/