PHP SQL列=列减去$ value

Question

I know how to add value within the SQL Query So current value of Bank = Bank + Value

UPDATE users SET Bank=Bank + '$deposit' WHERE Username='".($_SESSION['username'])."'"

As Example if $deposit = '500' so string/text = 500 and Example Bank value is 1000 it is 1500 right. Now i try to substract with current value.

UPDATE users SET Bank=Bank + '-500' WHERE Username='".($_SESSION['username'])."'"

Should be working. What not works is:

UPDATE users SET Bank=Bank + '-' + '$deposit' WHERE Username='".($_SESSION['username'])."'"

or

UPDATE users SET Bank=Bank + '-$deposit' WHERE Username='".($_SESSION['username'])."'"

What should i do?

Alright i've sold it myself, thanks for everyone that tried to help, ya'll brought me on the idea of the answer :

UPDATE users SET Bank=Bank +- '$deposit' WHERE Username='".($_SESSION['username'])."'

instead of only using

-

ive used

+-

Thanks.

Answer 1

您为什么不只使用-进行减法：

"UPDATE users SET Bank = Bank - $deposit WHERE Username = '{$_SESSION['username']}'"