Optional parameter

[donboe]

I’m working on a billing system where the customer ID either needs to be sent to the next page if it is an existing customer and not been sent when it is a new customer in which case the newly added customer ID is applicable. I thought that the use of an Optional paramater would do the trick. This is what I have right now:

Model

public function klant_gegevens($klant_id = '')
{
    $sql    =    "SELECT *
                   FROM `klant_gegevens`";
                        
    if ($klant_id)
    {
        $sql   .= "WHERE `klant_id` = ?";
        $stmt   =    $this->pdo->prepare($sql);
        $stmt->execute(array($klant_id));
    }
    else
    {
        $sql .= "ORDER BY `klant_id` DESC
                    LIMIT 1";
                        
        $stmt = $this->pdo->query($sql);            
    }         
        
    return $stmt->fetch();        
}

Controller

public function product_zoekenAction()
{
    if (isset($klant_id))
    {
        $klant_id = filter_input(INPUT_POST, 'klant_id', FILTER_SANITIZE_NUMBER_INT);
    }
    else
    {
        $klant_id = '';
            
    }

    $klant_gegevens = $this->administratie->klant_gegevens($klant_id);
        
}

However, this works only partially. Whenever I add a new client to the system, on the next page where I can add products to the invoice, I get the right customer information. However, when I use an existing customer that I choose from a dropdown menu I always get the information from the customer with the highest id

ORDER BY `klant_id` DESC LIMIT 1

What am I doing wrong. Thank you in advange

[droopsnoot]

Would this line evaluate as true?

    if (isset($klant_id))

as you haven’t created that variable until within either of the if conditions?