mysql自定义函数执行出错

在mysql5.0里创建了一函数代码如下：
DELIMITER $$;

DROP FUNCTION IF EXISTS `newspaper`.`f_hzcode`$$

CREATE FUNCTION `f_hzcode`() RETURNS char(1)
BEGIN
declare fpy char(1);
  declare pc char(1);
  declare cc char(4);
  set @fpy = UPPER(left(words,1));
  set @pc = (CONVERT(@fpy  USING  gbk));
  set @cc = hex(@pc);
  if @cc >= "8140" and @cc <="FEA0" then
    begin
      select PY from tbl_py where hz>=@pc limit 1 into @fpy;
    end;
  end  if;
  Return  @fpy;
END$$

DELIMITER ;$$

执行查询：
select f_hzcode('在');

出错提示：
错误代码: 1318
Incorrect number of arguments for FUNCTION newspaper.f_hzcode; expected 0, got 1
(耗费 0 ms)

什么原因？？？

---

1.  DELIMITER $$;
2.  DELIMITER ;$$
3.  CREATE FUNCTION `f_hzcode`() RETURNS char(1) DETERMINISTIC

SQL code:
mysql> DELIMITER $$
mysql>
mysql> DROP FUNCTION IF EXISTS `newspaper`.`f_hzcode`$$
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql>
mysql> CREATE FUNCTION `f_hzcode`() RETURNS char(1) DETE