如何使用下拉选项过滤页面？

I have a web page that displays a list of people and their nationality.

<td><?php echo $row['First_Name'] . " " . $row['Last_Name'] ?></td>

<td><?php echo $row['Country'] ?></td>

I would like to add a control to the page that allows the user to apply a filter on the country.

Any suggestions on how I should go about it?

You could make a link to the country - for instance like this:

//Change it, so it fits for your purpose    
<a href="file.php?filter=country">Filter by country</a>. 

And the PHP could simply look like this:

<?php

$con = mysql_connect("localhost","user","pass"); 
if (!$con) { 
    die('Could not connect to mysql server');
} 
mysql_select_db("thepoolscene", $con); 

$filterBy = ( isset( $_GET['filter']) ? 'country' : 'ASC');
$result = mysql_query("SELECT * FROM tblPlayers ORDER BY $filterBy");

?>