$customer = $_POST['customer'];
$statement = $connection->prepare($sql);
$statement->bindParam(':customer', $customer, PDO::PARAM_STR);
$statement->bindValue(':total_value', $total_value, PDO::PARAM_INT);
$statement->bindValue(':total_balance', $total_balance, PDO::PARAM_INT);
$statement->execute();
$result = $statement->fetchAll();
$total_value_result = $statement->fetch_assoc;

$sum = array_sum(array_column($total_value_result, 'total_value_result'));
    echo $sum['total_value'];