由于某种原因无法对插入进行多次评论

I have made a comment section for my gallery , but not sure sure why only able to do 1 comment on it then it wont allow me to execute any more comment on that item

the insert

public function insertComment() {
    if(!get_magic_quotes_gpc()) {
        $this -> sanitizeInput();   
    }        
    extract($_POST);

    $name = $_SESSION['userName'];
    $comment = $_POST['comment'];
    $productID = $_GET['id'];

    echo $name;
    echo $comment;
    echo $productID;


    $qry = "INSERT INTO comments VALUES (NULL, '$name', '$comment', '$productID' )";

    $rs = $this -> db -> query($qry);

    if($rs && $this -> db -> affected_rows > 0) {
        $msg = 'comment record created. ';
        } else {
        echo 'Error inserting comment';
    }
    return $msg;      
}

tables

Field   Type    Collation   Attributes  Null    Default Extra   Action
    id  int(11)         No  None    auto_increment                          
    name    varchar(150)    latin1_swedish_ci       No  None                                 
    comment varchar(150)    latin1_swedish_ci       No  None                                 
    productID   int(11)         No  None

maybe this will work

$qry = "INSERT INTO comments (name, comment, productID) VALUES ('$name', '$comment', '$productID' )";

remove the null