Troll

$query = $conn->prepare('SELECT * FROM '.$tb['msg'].' WHERE ('.$msg['to'].' = :partner
                AND  '.$msg['from'].' = :u_id) OR ('.$msg['from'].' = :partner
                AND  '.$msg['to'].' = :u_id) ORDER BY '.$msg['time'].' LIMIT (
                (SELECT COUNT('.$msg['id'].') FROM '.$tb['msg'].' WHERE
                ('.$msg['to'].' = :partner AND  '.$msg['from'].' = :u_id)
                OR ('.$msg['from'].' = :partner AND  '.$msg['to'].' = :u_id)),
                ((SELECT COUNT(*) FROM '.$tb['msg'].' WHERE ('.$msg['to'].' = :partner
                AND  '.$msg['from'].' = :u_id) OR ('.$msg['from'].' = :partner
                AND  '.$msg['to'].' = :u_id)) - 20)) ');