如何使用php动态回显日期范围搜索结果中列数据的总和？

I have a search feature that displays records from a database based on date range search. What I want to do is echo the total sum of the "refund_amount" column that is displayed after the date range search. I know how to get the total sum from all the records from the database. I need to echo only the sum of the "refund_amount" column that is being displayed after the date range search. Any help is greatly appreciated.

Here is my code:

<?php
  include('includes/connect.php');
  if (isset($_GET["status"])) { $status  = $_GET["status"]; } else { $status=0; };
  if (isset($_GET["d1"])) { $d1  = $_GET["d1"]; } else { $d1=0; };
  if (isset($_GET["d2"])) { $d2  = $_GET["d2"]; } else { $d2=0; };
  $result = $connect->prepare("SELECT * FROM rma_list WHERE refund_date BETWEEN :a AND :b");
  $result->bindParam(':a', $d1);
  $result->bindParam(':b', $d2);
  $result->execute();
  for($i=0; $row = $result->fetch(); $i++){
  ?>

  <tr class="record">
  <td><?php echo $row['rma_id']; ?></td>
  <td><?php echo $row['order_date']; ?></td>
  <td><?php echo $row['rma_request_date']; ?></td>
  <td><?php echo $row['rma_number']; ?></td>
  <td><?php echo $row['order_number']; ?></td>
  <td><?php echo $row['so_number']; ?></td>
  <td><?php echo $row['vendor_name']; ?></td>
  <td><?php echo $row['vendor_ra']; ?></td>
  <td><?php echo $row['customer_name']; ?></td>
  <td><?php echo $row['credit_memo_number']; ?></td>
  <td><?php echo $row['refund_amount']; ?></td>
  <td><?php echo $row['refund_date']; ?></td>
  <td><?php echo $row['status']; ?></td>
  </tr>



  <?php
  }
  ?>

To do this in PHP code

<?php
include('includes/connect.php');
if (isset($_GET["status"])) { $status  = $_GET["status"]; } else { $status=0; };
if (isset($_GET["d1"])) { $d1  = $_GET["d1"]; } else { $d1=0; };
if (isset($_GET["d2"])) { $d2  = $_GET["d2"]; } else { $d2=0; };
$result = $connect->prepare("SELECT * FROM rma_list WHERE refund_date BETWEEN :a AND :b");
$result->bindParam(':a', $d1);
$result->bindParam(':b', $d2);
$result->execute();

// initialise a variable for the counter
$tot = 0;

while ($row = $result->fetch(PDO::FETCH_ASSOC)){
?>
      <tr class="record">
          <td><?php echo $row['rma_id']; ?></td>
          <td><?php echo $row['order_date']; ?></td>
          <td><?php echo $row['rma_request_date']; ?></td>
          <td><?php echo $row['rma_number']; ?></td>
          <td><?php echo $row['order_number']; ?></td>
          <td><?php echo $row['so_number']; ?></td>
          <td><?php echo $row['vendor_name']; ?></td>
          <td><?php echo $row['vendor_ra']; ?></td>
          <td><?php echo $row['customer_name']; ?></td>
          <td><?php echo $row['credit_memo_number']; ?></td>
          <td><?php echo $row['refund_amount']; ?></td>
          <td><?php echo $row['refund_date']; ?></td>
          <td><?php echo $row['status']; ?></td>
      </tr>
<?php

    // accumulate the amount in the new var
    $tot += $row['refund_amount'];
}
?>
    <tr class="totals">
        <td colspan="10"> TOTAL Refund</td>
        <td><?php echo $tot; ?></td>
        <td colspan="2">&nbsp;</td>
    </tr>

The table layout may need a little work, but I hope you get the idea from this code