Руслан

$q = $db->prepare('SELECT * FROM `users` LIMIT :limit');
$q->bindValue(':limit', $_POST['ot_max'], PDO::PARAM_INT);
$q->execute();

while ($row = $q->fetch(PDO::FETCH_ASSOC)) {
    echo $row['real_name'] . ": " . result($row['id']);
}