Insert NULL into database with pdo

Question

in the database I'm working with, there's a table named "packets", in this table there are columns like "id", "userid" etc. and a column named "usage"(I know its a poor choice of name cause usage is a reserved word, but sadly I may not change anything in the table), the type of this column is enum with 3 values("education", "study" and "advanced training") with "education" as default-value and the value can be NULL.

I wrote a class Packet with getters/setters like set_usage($usage)/get_usage() and a class Packet_dao for accessing database using pdo:

class Packet_dao {
    private m_insert_query;
    ...
    public function persist($data)
    {
        $query = $this->m_insert_query;
        try
        {
           $stmt = $this->bind_param($data, $query);
           $stmt->execute();
           return true;
        }
        catch (PDOException $ex)
        {
           $this->m_error_message = $ex->getMessage();
           return false;
        }
    }

    private function bind_param($packet, $query)
    {
       $stmt = $this->m_pdo->prepare($query);
       $stmt->bindParam(':userId', $packet->get_user_id());
       ...
       $stmt->bindParam(':usage', $packet->get_usage());
       return $stmt;
    }

insert query would looks like

INSERT INTO packets (userId, number, ..., `usage`) 
VALUES (:userId, Coalesce(:number, default(number)), Coalesce(:usage, default(`usage`)))

so if I want to add a packet into db, the code would looks like:

$packet = new Packet();
$packet_dao = new Packet_dao();
$packet->set_stuff("stuff");
$packet_dao->persist($packet);

so far, so good, everything is working fine.

now, another usage-case "fullversion" should be added, and instead of adding a new value to the enum, they decided to use NULL as value of usage for packets which are full version. Now I get a problem: when I try to set value for usage using $packet->set_usage(NULL) , it will be interpreted as the same as if the value isn't set and the default value("education") will be set in this case. What should I do?

Answer 1

apparently, the 2nd parameter of Coalesce() force it to take the default value when nothing is set (or NULL), after I changed Coalesce(:usage, default(usage)) into :usage . It worked