您不能通过绑定输入行名.更改为:

you cant put row-name via bind. change it to:

   try {
        $sql = "SELECT $page FROM roles WHERE role = :role";
        $s = $pdoUsers->prepare($sql);
        $s->bindValue(":role", $role);
        $s->execute();
    } catch (PDOException $e) {