创建两个会话之一的PHP

Im trying to create two different sessions. One for the admin, the other for normal users. If SQL returns admin_role as 1 = admin. If admin_role as 0 = user.

I have session_start() in the beginning of the document via include('connection.php'). When I press submit on my login form nothing really happens as for now.

if(empty($_POST["username"]) || empty($_POST["password"])){
    $error = "Fill in both fields!";
} else {
    // Define $username and $password
    $username=$_POST['username'];
    $password=$_POST['password'];

    // To protect from MySQL injection
    $username = stripslashes($username);
    $password = stripslashes($password);
    $username = mysqli_real_escape_string($db, $username);
    $password = mysqli_real_escape_string($db, $password);

    // Check username and password from database
    $sql = "SELECT admin_role FROM user WHERE user_name='$username' AND user_password='$password'";
    $result = mysqli_query($db, $sql);

    $admin_role = $row['admin_role'];

    // If username and password exist in our database then create a session.
    // Otherwise echo error.
    if(mysqli_num_rows($result) == 1){
        if($admin_role == 1){
            $_SESSION['admin'];
            header("location: logged-in.php");
        }
        if($admin_role == 0){
            $_SESSION['username'];
            header("location: logged-in.php");
        }

    } else {
        $error = "Wrong credentials";
    }
}