MySQL库数据库存储过程

我有一个存储过程，它应该从虚构的图书馆数据库中借书，该过程应该检查该书是否可用，然后检查用户是否超过其限制，然后减少我知道的图书表中所选图书的可用拷贝数，这也不是我在返回一个字符串来判断这个过程是否顺利执行之前，如何布局数据库并创建一个新的贷款。程序如下：

delimiter $$
create procedure BorrowBook(in theBookID int, in theUserID int)
begin
declare lim int;
declare num int;
declare loanNumber int;
declare copyNumber int;
set lim = (select Readers.Limit from Readers where Readers.id = theUserID);
set num = (select Count(*) from Loans where Loans.UserID = theUserID);
set loanNumber = (select Count(*) from Loans) + 1;
set copyNumber = (select NumberAvailable from Book where Book.id = theBookID);
if(copyNumber > 0)
then
if(num<lim)
then
insert into Loans values(loanNumber, theBookID, theUserID, curDate(), 0);
commit;
update Book set Book.NumberAvailable = Book.NumberAvailable - 1 where Book.id = theBookID;
select 'Succesful Update';
else
rollback;
select 'Borrow limit reached';
end if;
else
rollback;
select 'No copies available';
end if;
end $$

它出现了错误

#1312 - PROCEDURE reddurrant_com.BorrowBook can't return a result set in the given context

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有人能告诉我为什么它不工作吗？欢呼声

可能相关：您是否在多选模式下操作？客户端\u多\u结果处于打开状态：

#1312 - PROCEDURE reddurrant_com.BorrowBook can't return a result set in the given context