how to get sum on every loop on the table - php

Question

I have a problem on breaking down the amount of the given payment, I think i was missing something on my code. This is my table below.
If i have payment of 5,000, it will deduct on the first row and the remaining sum will send to the 2nd row.
//this is the payment
$payment = 5000;
$temp = '';
//the loop of function
$data = payment_breakdown();
foreach ($data as $row) {
$amount = $row['AMOUNT'] - $payment."\n";
}
//handle the difference of every loop of the function
$temp = $amount;
//result of the amount
echo $amount;
//this is my function to get the data from the table
function payment_breakdown(){
$db = database2();
$query = "SELECT AMOUNT FROM TABLE1";
$cmd = $db->prepare($query);
$cmd->execute();
$rows = $cmd->fetchAll();
$db = null;
return $rows;
}
supposedly if the amount on the table is this
Data From Table | The Payment
3000 | 3000
3000 | 2000

Answer 1

You could do it in SQL:
SELECT
amount,
paid,
sum(amount-paid) open
FROM
payment
GROUP BY amount, paid
WITH ROLLUP
HAVING
amount IS NULL
OR paid IS NOT NULL
;
Based on the data
INSERT INTO payment (amount, paid)
VALUES
(3000,3000),
(3000,2000),
(4000,1000)
;
you get
amount;paid; open
3000 ;2000; 1000
3000 ;3000; 0
4000 ;1000; 3000
NULL ;NULL; 4000
Or you might want a simple substraction from a deposit:
SET #credit := 5000;
SELECT
amount,
#credit := #credit-amount credit
FROM payment
;
SELECT #credit;
However, in the latter case you should rather store all payments and amounts to pay into database tables and sum up all together. Consider refactoring your database structure design.