Getting only last message for each user - php

Question

I am doing PM system for my site. I created subpage for each conversation by two users. I am having hard time programming the front page, where all conversations are printed. I cant get only one and last meassage for each user.
Here is my function:
public function fetch_data($id_uporabnika) {
global $pdo;
$query = $pdo->prepare("SELECT * FROM zs WHERE za = ? ORDER BY datum");
$query->bindValue(1, $id_uporabnika);
$query->execute();
return $query->fetchAll();
}
And here is my code for printing conversations:
<?php
} else {
$zs = new Zs;
$id_uporabnika = $trenutni['id'];
$zsji = $zs->fetch_data($id_uporabnika);
?>
<h2>Zasebna sporočila</h2>
<ul class="vsi-zsji">
<?php foreach ($zsji as $sporocilo): ?>
<?php $od = $oseba->fetch_data($sporocilo['od']) ?>
<li>
<a href="<?php echo $url; ?>zs/poglej/<?php echo $sporocilo['od']; ?>">
<img src="<?php echo $url; ?>inc/timthumb.php?src=<?php echo $od['slika_potem'] ?>&w=60&h=60" alt="">
<p><b><?php echo $od['uporabnisko_ime'] ?></b></p>
<p><?php echo $sporocilo['vsebina'] ?></p>
</a>
</li>
<?php endforeach ?>
</ul>
<?php } ?>
I get 10 PMs from one user, 3 for another. I want to display just the latest one.

Answer 1

Just put a LIMIT clause in your SQL query and order by DESC to get the latest message:
$query = $pdo->prepare("SELECT * FROM zs WHERE za = ? ORDER BY datum DESC LIMIT 1");

Answer 2

something like this should help
SELECT id,datum, max(pm) FROM zs WHERE za = ? group by id,datum