mysql定义触发器异常，[Err] 1415 – Not allowed to return a result set from a trigger

mysql定义触发器错误，：[Err] 1415 – Not allowed to return a result set from a trigger

DROP TRIGGER IF EXISTS t_afterupdate_on_borrowinfo; 

CREATE TRIGGER t_afterupdate_on_borrowinfo  

AFTER UPDATE ON borrowinfo  

FOR EACH ROW 

BEGIN

 DECLARE day int;

  select to_days(curdate())-to_days (back_date )as day from borrowinfo;

  update borrowinfo set overdue_day=days where day>0;

 update borrowinfo set fines=days*0.1 where day>0;

END;

定义了一个触发器，目的是：当当前日期超过应归还日期时，把表中的过期天 置为两个日期的差值，罚款 为fines=days*0.1 、、、

执行后错误是：[Err] 1415 – Not allowed to return a result set from a trigger

求指导，刚接触mysql，写的乱七八糟

select to_days(curdate())-to_days (back_date ) into day from borrowinfo;

PHP code

DROP TRIGGER IF EXISTS t_afterupdate_on_borrowinfo; 
CREATE TRIGGER t_afterupdate_on_borrowinfo  
AFTER UPDATE ON borrowinfo  
FOR EACH ROW 
BEGIN
 DECLARE day int;
  select to_days(curdate())-to_days (back_date )into day from borrowinfo;
  update borrowinfo set overdue_day=day where day>0;
 update borrowinfo set fines=day*0.1 where day>0;
END;