php - How to Minus 2nd row value from the 1st row in same HTML table

Question

I'm struggling with a PHP Code, and I have no clue how to solve this. I have two columns with timestamps on which I've ordered by desc in my Html table which I'm generating with PHP code.

I need to find out the differences between the 2nd row StateEndTime and the 1st-row StateStarTtime nd so on and display this in a new row/column. The final table should look like this :

ID          Type         StateStarTtime    StateEndTime   Min Difference

xxx         YYY          03:57             03:59          00:02
xxx         ZZZ          03:53             03:55          00:04
xxx         ZZZ          03:46             03:49          

Below is the PHP code in my index file

<?php while($row = mysqli_fetch_array($search_result)):?>
  <tr>
      <td align="Center"><?php echo $row['id'];?></td>
      <td align="Center"><?php echo $row['Username'];?></td>
      <td align="Center"><?php echo $row['StateStarttime'];?></td>
      <td align="Center"><?php echo $row['StateEndtime'];?></td>
      <?php endwhile;?>

Answer 1

    <?php 
    $lasttime = 0;
    while($row = mysqli_fetch_array($search_result)):?>
    <tr>
      <td align="Center"><?php echo $row['id'];?></td>
      <td align="Center"><?php echo $row['Username'];?></td>
      <td align="Center"><?php echo $row['StateStarttime'];?></td>
      <td align="Center"><?php echo $row['StateEndtime'];?></td>
      <td align="Center"><?php echo ($row['StateStarttime'] - $lasttime);?></td>
      <?php 
$lasttime = $row['StateStarttime'];
endwhile;?>