Issue sorting inside while loop - php

Question

I have a strange issue happening. I've got a table where I want to order the number of times a product was sold. I'll post the query, but the issue is inside the while loop.
Query:
$cat = $db->query("SELECT *, COUNT(id_produto) as quantos FROM produtos p JOIN pedidos m ON p.id_prod = m.id_produto GROUP BY id_produto ORDER BY quantos +0 DESC");
$cat->execute();
Now the loop:
while($res_cat = $cat->fetch(PDO::FETCH_ASSOC)){
$quantidade_ok = $res_cat['quantos'] * $res_cat['qtde'];
$quanti = array($quantidade_ok);
rsort($quanti);
foreach($quanti as $ord){
echo $ord."<br>";
}
The output is:
40
50
4
1
3
2
10
But I want it to be:
50
40
10
4
3
2
1
I'll be happy for any help.

Answer 1

You're sorting within a loop (so your sorting already happened), and you're sorting an array with just 1 value $quanti, so your sort does nothing.
You have 2 ways to approach this properly: edit your query to actually sort how you wish, or sort the PHP array before looping it.
Option 1: Edit your query
Based on your code it seems clear that you wish to sort by the product of quantos times qtde. So you can simply edit your query as follows:
SELECT *, COUNT(id_produto) as quantos
FROM produtos p JOIN pedidos m ON p.id_prod = m.id_produto
GROUP BY id_produto
ORDER BY (quantos*qtde) DESC
Option 2: Sort via PHP
If you prefer to sort via PHP as you don't want to change your query, you can simply populate a temporary array, the product of quantos times qtde as key and then use krsort to sort the array.
In code:
$array = [];
while ($res_cat = $cat->fetch(PDO::FETCH_ASSOC)) {
$key = $res_cat['quantos'] * $res_cat['qtde'];
$array[$key] = $res_cat;
}
krsort($array);
foreach ($array as $ord => $res_cat) {
echo $ord."<br>";
}

Answer 2

You overwrite $quanti each time so it always has a single value.
Try this:
$quanti = [];
while($res_cat = $cat->fetch(PDO::FETCH_ASSOC)) {
$quantidade_ok = $res_cat['quantos'] * $res_cat['qtde'];
$quanti[] = $quantidade_ok;
}
rsort($quanti);
foreach($quanti as $ord){
echo $ord."<br>";
}