php - Check specific MySQL value and print/delete recursively

one text

I want to check a single MySQL cell from a column periodically (every 30 min) and print it on localhost in order to use this page as a browser source on OBS studio. Once the value changes, I want to delete the previous one and print the new one, so the output is only the current value of the cell.

Right now, I am able to connect to my database with index.php, check a column, and print it once, but I'm having trouble adding an infinite loop and a way to delete the previous value once it changes. I've tried adding a while(1){} in conjunction with sleep(), but the page just never loads and nothing gets printed.

My code now:

<?php
include_once 'index.php';
$result = mysqli_query($conn,"SELECT username FROM realrobot_db.realrobot_dashboard");
?>

<!DOCTYPE html>
<html>
 <head>
 <title> Retrieve data</title>
 </head>
<body>

<?php
if (mysqli_num_rows($result) > 0) {
?>

<table>

<?php
$i=0;
while($row = mysqli_fetch_array($result)) {
?>

<tr>
    <td><?php echo $row["username"]; ?></td>
</tr>

<?php
$i++;
}
?>

</table>

 <?php
}
else{
    echo "No result found";
}
?>
 </body>
</html>

Source