I'm basicly working with mysql update here.

So i have a table called users and a field named money.
now when user register he also register's an amount of hidden input of money.
input sent to mysql table>money(field)>amount.

now what i want is that if he presses a button, it will decrease his amount of money in the sql.and the button he press will give him something like 500$ for a candy.
so to a field named candy the update will make it (1) and money from the basic amount will get decreased.

can someone help me make the code?