Question

我有一个问题，我曾试过谷歌，但尚未找到答案。我想要做的是使用存储过程在MySQL中的两个帐户之间转移资金。例如，如果我使用呼叫转移（20，'测试'，3,5）。然后我将从accountID 3转移20美元到accountID 5并写下消息“Test”，这是应该做的。

然而，此时可以在不存在的帐户之间汇款，并且对于发送帐户ID，金额可以是<0，例如呼叫转移（20000000，'测试'，34,54）。

有谁知道如何解决这些问题（金额必须> = 0且只有现有的帐户ID可以接收和汇款）？我正在使用的代码可以在下面找到：

创建表格：

Create table Account 
(
AccountID int AUTO_INCREMENT primary key 
,amount decimal check (amount >= 0));

Create table Transfers 
(
TransfersID int AUTO_INCREMENT primary key
,amount decimal
,from_account_id int not null
,to_account_id int not null
,note varchar(50) not null
,datetime datetime not null
,Constraint from_account_key foreign key (from_account_id) references 
Accounts (id)
,Constraint to_account_key foreign key (to_account_id) references Accounts 
(id)
);

insert into accounts (id, amount) values (1, (rand()*100));
insert into accounts (id, amount) values (2, (rand()*100));

创建存储过程：

delimiter //
create procedure transfer (amount int, note varchar(50), sending_account 
int, receiving_account int)
begin

start transaction;
update accounts as A
set A.amount = A.amount - amount
where A.AccountID = sending_account;

update accounts as A
set A.amount = A.amount + amount
where A.AccountID = receiving_account;

insert into transfers values 
(TransfersID, amount, sending_account, receiving_account, note, now());
commit work;

end //
delimiter ;

Answer 1

在过程开始时添加了对金额的检查，并在insert into transfers语句之前移动了update。 transfers表引用account表中有外键，因此如果您尝试插入不存在的id，它将立即失败。

delimiter //
create procedure transfer (amount int, note varchar(50), sending_account 
int, receiving_account int)
this_proc:begin 

start transaction;

if amount <= 0 then
    leave this_proc;
end if;

insert into Transfers values 
(TransfersID, amount, sending_account, receiving_account, note, now());

update Account as A
set A.amount = A.amount - amount
where A.AccountID = sending_account;

update Account as A
set A.amount = A.amount + amount
where A.AccountID = receiving_account;

commit work;

end //
delimiter ;

在MySQL

1 个答案: