only echo repeated mysql row once

I am trying to figure out a way I can echo a repeated piece of data in my SQL database only once. Here is what I mean:

$user = $_SESSION['name'];

while ($result = $sql->fetch_array()) { 
                    $user_from = $result['user_from'];
                    $user_to = $result['user_to'];

                    $messages = new ArrayObject(array());

                    if ($user_from !== $user) {
                        $messages->append($user_from);

                        foreach ($messages as $messages_from) {
                                echo "<a id='messages' href='../private/" . $messages_from ."'>" . $messages_from . "</a><hr>";
                        }
                    }
                    if ($user_to !== $user) {
                        $messages->append($user_to);

                        foreach ($messages as $messages_to) {
                                echo "<a id='messages' href='../private/" . $messages_to ."'>" . $messages_to . "</a><hr>";
                        }
                    }
                }

This is my code. In my database:

id | messages | user_from | user_to

1  |   hi     |    John   | Alex
2  |   hey    |    Alex   | John

The code above is displaying John twice (because I am logged in as Alex). How do I only make it display John once?

Thanks in advance

Alex