while ($row = mysqli_fetch_array($result)) {
$i++;
$sku = $row['sku'];
$quantity= $row['quantity'];
$stack += [$sku=>$quantity];
//array_push($stack,[$sku=>$quantity]);
}
$stack_sum = array_count_values($stack);
foreach ($stack_sum as $key => $value)
{
echo "<li><font color=\"#6c6874\"><b>$key:</b></font> $value</li>";
}