PDO选择最大查询不返回任何内容，空白页

Question

So I have a function within a class to take the highest value based on another value but I'm getting a blank page.

I checked for bad syntax but there's none that the validator found and if I change it to header("Location: https://facebook.com") it will go to the site so it seems the function is working. However I am not getting my variable back.

My connections and everything else are fine as my other functions in this class return what I want.

class FORUM
{
    private $forum;

    function __construct($DBFORUM_con)
    {
        $this->db = $DBFORUM_con;
    }

    public function addCount($id)
    {
        try
        {   
            $stmt = $this->db->prepare("SELECT MAX(a_id) AS Maxa_id FROM forum_answer WHERE question_id = :id");

            $stmt->execute(array(':id'=>$id));
            $userRow = $stmt->fetch(PDO::FETCH_ASSOC);

            if ($stmt->rowCount() > 0)
            {
                $Max_id = $userRow['Maxa_id'] + 1;

                return $Max_id;
            }
            else {
                $Max_id = 1;

                return $Max_id;
            }
        }
        catch(PDOException $e)
        {
            echo $e->getMessage();
        }
    }
}

Then in my page that processes the form:

//require class

$id = $_POST['id'];

if ($forum->addCount($id))
{
    echo $Max_id;
}
else
{
    echo $Max_id;
}

Answer 1

You're not assigning the return value to anything.

Try

$id = $_POST['id'];

$Max_id = $forum->addCount($id)

if ($Max_id)
{
    echo $Max_id;
}
else
{
    echo $Max_id;
}