trigger 出错

delimiter //
create trigger station_info_trigger
before insert on station_info
for each row
Begin
If new.station_group1 is null then
set new.station_group1 = new.station_id;
END IF;
end;//
delimiter ;
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我的sql语句如上所示。
mysql的版本是5.0的。
但是执行之后下面的错误是啥原因呢？？？
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mysql> delimiter //
mysql> create trigger station_info_trigger
    -> before insert on station_info
    -> for each row
    -> Begin
    -> If new.station_group1 is null then
    -> set new.station_group1 = new.station_id;
    -> END IF;
    -> end;//
ERROR 1235 (42000): This version of MySQL doesn't yet support 'multiple triggers
with the same action time and event for one table'
mysql> delimiter ;

http://dev.mysql.com/doc/refman/ ... html#using-triggers