图书馆管理系统里的一个小问题

[qq_37698963]

--计算某读者已借几本书
Create or replace function f_borrowed_num(v_readerid number)
return number
as
V_num number;
Begin
Select count(*) into v_num from reader,borrow where reader.readerid=v_readerid and reader.readerid=borrow.readerid;
Return v_num;
End;


--利用自定义函数写一个只要在borrow表上有变动时就进行更新rest_borrow_num的触发器
create or replace trigger tr_update_borrow
after update or delete or insert on borrow
for each row
declare
v_rule rule%rowtype;
cursor cur_rule is (select readerid from reader);
begin
select * into v_rule from rule ;
for v_readerid in cur_rule loop
update reader set rest_borrow_num=v_rule.num-f_borrowed_num(v_readerid)
where v_readerid=:old.readerid and reader.readertype=v_rule.readertype;
end loop;
End;
/
此时报错：错误(270,61): PLS-00382: 表达式类型错误
求大佬们告知我原因和如何改正！！！谢谢。

[卖水果的net]

select * into v_rule from rule ; 这是要查出来多行，怎么办 ？

[qq_37698963]

嗯，rule的确不止只一条，难道用双重游标循环吗，这个我不太会；试了一下 create or replace trigger tr_update_borrow after update or delete or insert on borrow for each row declare cursor cur_reader is select readerid from reader; cursor cur_rule is select * from rule ; begin for v_readerid in cur_reader loop for v_rule in cur_rule loop update reader set rest_borrow_num=v_rule.num-f_borrowed_num(v_readerid) where v_readerid=:old.readerid and reader.readertype=v_rule.readertype; end loop cur_reader; end loop cur_rule; End; / 但还是报同样的错误。