mysql的触发器,官网教程都有错.望解决

用户表:
create table user(
    u_id int unsigned auto_increment primary key,
    u_name char(15)
)type=myisam default charset utf8 collate utf8_general_ci;



帖子表:
drop table post;
create table post(
    p_id int unsigned auto_increment primary key,
    u_id int unsigned,
    p_title varchar(180),
    p_content text
)type=myisam default charset utf8 collate utf8_general_ci;

/*** 如果存在则删除触发器 ***/
drop trigger if exists trg_user_delete;
/*** 创建触发器 **/
create trigger trg_user_delete
before delete 
on user
for each row
begin    
    /****定义一个变量用于存储删除的用户主键ID***/
    declare before_u_id int;
    /****赋值***/
    set before_u_id = old.u_id;
    delete from post where u_id = before_u_id
end;