更新数据库中的付款 [英] Update Payment in database

问题描述

我使用更新查询来更新付款方式

I use update query to update the payment

SqlCommand cmd = new SqlCommand(UPDATE Bank SET Payment = (Payment - '"+tprice.Text +"') WHERE NICNO = '" + FN.Text + "'", con);

将会发生以下错误
操作数数据类型nvarchar对于减法运算符无效.

the following error will occur
Operand data type nvarchar is invalid for subtract operator.

推荐答案

该错误表示它的含义.您将价格文本框的内容括在引号中，从而使其成为字符串.另外，如果输入非数字，您的代码也会爆炸，并且如果有人聪明，由于SQL注入，他们可以使用您的代码擦除整个数据库.

The error means what it says. You''re putting the contents of the price textbox in quotes, which makes it a string. Also, your code will blow up if a non number is entered, and if someone is smart, they can use your code to erase your entire DB, due to SQL injection.

添加值参考的价格
cmd.parameter.addwithvalue("@ payment"，tprice.text)

add value reference of tprice
cmd.parameter.addwithvalue("@payment", tprice.text)

我的疯狂猜测是您正在尝试这样做-

My wild guess is this is what you are trying to do -

SqlCommand cmd = new SqlCommand("UPDATE Bank SET Payment = '(Payment - "+tprice.Text +")' WHERE NICNO = '" + FN.Text + "'", con);

看看是否有帮助.

see if it helps.

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