public function destroy($sessionId){
        //si la sesión está abierta y tengo lock 
        if($this->opened){
            $sql= $this->connection->connection->prepare('DELETE FROM sessions WHERE session_id = :id');
            $sql->bindValue('id', $sessionId);
            return $sql->execute() === TRUE;
        }
        else{
            return FALSE;
        }
    }