MYSQL,触发器,实现多个表共用ID不重复

DROP TRIGGER IF EXISTS `InsertUser`;
create trigger InsertUser    
before insert on userinfo   
for each row    
Begin   

declare id int;
insert into user values (NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL);#让自动增长的表插入失败,ID作废,就可以让触发器的表使用
select id  into @id from user order by id desc limit 1;

set new.id = @id;

end;