Problems inserting negative numbers in MySQL with PHP - php

Question

I am trying to build a simple web app to keep up with my debt and I want to use the same database table for adding and also subtracting data.
I am converting the input from the input field using a simple php operation to convert it to a negative number:
$sum2 = $sum*-1;
$sum being the input field:
$sum = $_POST['shuma'];
The Idea is, when I input a positive number, my debt grows larger, when I input a negative number, my debt gets smaller, it's a simple idea.
In MySQL database, I am inserting the input into:
decimal(7,2) Default:Null
The problem is, the positive input, even though it's being converted into a negative number, it's not being inserted as negative in MySQL, it inserts it again with a positive number. The problem it's not within PHP because I tested it and even after the form it's submitted and data it's pushed into MySQL, I still can get the negative number shown using the echo in PHP.
Does anyone have any idea how to solve this?
P.S. Maybe I should mention, when I try to insert negative directly from phpmyadmin it works, it accepts the negative number in the same field.
Thank you.

Answer 1

change you field type to DECIMAL (10,2) . Field length defination is on you. Define length according to your requirement.
In this case negative value will be inserted. If not, then please die(); your query and execute it directly in mysql. Because for another field's problem also negative value not insert in table though the field type is DECIMAL.

Answer 2

Well, I am trying to use the same input field for both, only use a
checkbox, when the box it's checked, it's a negative number, otherwise
it's positive
About that comment.
i.e. you have
<input type="checkbox" name="negative"/>
<input type="text" name="sum" />
<?php
$sum = (int)$_POST['sum'];
...
so you can have, let's say two methods:
function increase($value) {
return query("UPDATE table SET value = value + $value");
}
and
function decrease($value) {
return query("UPDATE table SET value = value - $value");
}
so you are checking:
if(isset($_POST['negative']) {
decrease($sum);
}
else {
increase($sum);
}
However, the queries are just a sample, I just wanted to explain the logic, where you don't need to add the number with negative sign, but you can change the query depends on the checked inputs