从数据库获取值，返回“bool(false)”

我的代码是这样的:

if(isset($_SESSION['id']) && isset($_SESSION['username'])){
    $user_status = $db->prepare("SELECT `user_status` FROM `users` WHERE `id` = :id AND `username` = :username");
    $user_status->bindValue(":id",$_SESSION['id'],PDO::PARAM_STR);
    $user_status->bindValue(":username",$_SESSION['username'],PDO::PARAM_STR);
    $user_status = $user_status->fetchColumn();
    if($user_status == 0){
        header("Location: /logout");
    }elseif($user_status == 8 || $user_status == 9){
        $links = '(<a href="/admin/index">Admin</a>)';
    }
}

当我做$user_status的var_dump时，当它应该说"1"时，它说"bool(false)"，因为这是数据库中的默认user_status。

我有登录脚本检查用户是否被禁止，这工作得很好:

$check_banned = $db->prepare("SELECT `user_status` FROM `users` WHERE `username` = :username");
$check_banned->bindValue(":username",$_POST['username'],PDO::PARAM_STR);
$check_banned->execute();
$check_banned = $check_banned->fetchColumn();