records met dezelfde waarde in EEN rij

<?php 
$result= $mysqli->query("SELECT * 
FROM `gelijke_datums` 
order by datum");
if ($mysqli->connect_errno) {
    printf("Connect failed: %s\n", $mysqli->connect_error);
    exit();
    }?>


 <?php while ($row = $result->fetch_array())
                 {                                
                $id = stripslashes($row['id']);                
                $datum = stripslashes($row['datum']);
                $activiteit = ($row['activiteit']);        
           ?>


 <p> <span><?php echo $datum ?></span> <a href="#<?php echo $id ?>" >
 <?php echo $activiteit ?></a> </p>
    <hr>
    <?php } ?>

<?php
$prevDate = null;
while ($row = $result->fetch_array()) {
    $id = stripslashes($row['id']);
    $datum = stripslashes($row['datum']);
    $activiteit = $row['activiteit'];
?>
    <p>
        <span><?= $datum ?></span>
        <a href="#<?= $id ?>"><?= $activiteit ?></a>
    </p>
    <?php if ($prevDate && $prevDate !== $datum) { ?>
    <hr />
    <?php }
    $prevDate = $datum;
}
?>

<?php
$prevDate = null;
while ($row = $result->fetch_array()) {
    $id = stripslashes($row['id']);
    $datum = stripslashes($row['datum']);
    $activiteit = $row['activiteit'];
    if ($prevDate && $prevDate !== $datum) { ?>
    <hr />
    <?php }
    <p>
        <span><?= $datum ?></span>
        <a href="#<?= $id ?>"><?= $activiteit ?></a>
    </p>
    <?php $prevDate = $datum; ?>
}
?>

<?php
$prevDate = null;
while ($row = $result->fetch_array()) {
    $id = stripslashes($row['id']);
    $datum = stripslashes($row['datum']);
    $activiteit = $row['activiteit'];?>
	
	<?php if($prevDate == $datum): ?>
		<a href="#<?= $id ?>"><?= $activiteit ?></a>
	<?php else:?>
		<hr />
		<span><?= $datum ?></span>
                <a href="#<?= $id ?>"><?= $activiteit ?></a>
	<?php endif;?>
	
	<?php $prevDate = $datum;?>
	
<?php } ?>