如何在php while循环中使用iframe打印页面

Question

How to print a page by using iframe inside php while loop

say I have a php code and javascript like this:

$qry=("SELECT * FROM tbl");
$result=mysqli_query($con,$qry);
while($test = mysqli_fetch_array($result))   {  ?>

<tr>
<td><?php echo $test['staff_id']; ?></td>
<td><?php echo $test['name']; ?></td>
<td><?php echo $test['rank']; ?></td>

<td><a href="#"  onclick="printPg()" >
<img src="src/img/print.jpeg" height="25" /></a>

<div id="printerDiv" style="display:none"></div>

<script>
function printPg()
{
    var div = document.getElementById("printerDiv");
    div.innerHTML = '<iframe src="print.php?id=<?php echo $test['sn']; ?>" onload="this.contentWindow.print();"></iframe>';
}
</script>

</td>
</tr>
<?php   }  ?>

If I click on print image in any row, it only prints the last row of the table.

Any help will be greatly appreciated.