/AjaxDropdownList.php

## AjaxDropdownList.php
//Index.php
<?php
$conn = mysql_connect("localhost", "root", "root");
$db = mysql_select_db("country_example", $conn);

$sql_country = "SELECT * FROM country";
$result_country = mysql_query($sql_country);

?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Country List</title>
</head>
<body>
<?php

echo "<select name='country' onChange='get_cities(this.value)'>";

while($row_country = mysql_fetch_array($result_country))
{
    echo "<option value='".$row_country['id']."'>".$row_country['country']."</option>";
}
echo "</select>";
echo "<div id='cityLayer'><select name='city' id='city'></select></div>";
?>
    <script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
    <script type="text/javascript">
    function get_cities($country_id){
     $.ajax({
         url : "city.php?country_id="+$country_id,
         cache : false,
         beforeSend : function (){
              //Show a message
         },
         complete : function($response, $status){
             if ($status != "error" && $status != "timeout") {
                 $('#cityLayer').html($response.responseText);
             }
         },
         error : function ($responseObj){
             alert("Something went wrong while processing your request.\n\nError => "
                 + $responseObj.responseText);
         }
     });
    }
 </script>
</body>
</html>

//City.php
<?php

$conn = mysql_connect("localhost", "root", "root");
$db = mysql_select_db("country_example", $conn);

$country_id = $_REQUEST['country_id'];
$sql_city = "SELECT * FROM cities WHERE country_id = '".$country_id."'";
$result_city = mysql_query($sql_city);

echo "<select name='city'>";
while($row_city = mysql_fetch_array($result_city))
{
    echo "<option value='".$row_city['id']."'>".$row_city['city']."</option>";
}
echo "</select>";
?>
	//Index.php
	<?php
	$conn = mysql_connect("localhost", "root", "root");
	$db = mysql_select_db("country_example", $conn);

	$sql_country = "SELECT * FROM country";
	$result_country = mysql_query($sql_country);

	?>
	<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
	<html xmlns="http://www.w3.org/1999/xhtml">
	<head>
	<title>Country List</title>
	</head>
	<body>
	<?php

	echo "<select name='country' onChange='get_cities(this.value)'>";

	while($row_country = mysql_fetch_array($result_country))
	{
	echo "<option value='".$row_country['id']."'>".$row_country['country']."</option>";
	}
	echo "</select>";
	echo "<div id='cityLayer'><select name='city' id='city'></select></div>";
	?>
	<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
	<script type="text/javascript">
	function get_cities($country_id){
	$.ajax({
	url : "city.php?country_id="+$country_id,
	cache : false,
	beforeSend : function (){
	//Show a message
	},
	complete : function($response, $status){
	if ($status != "error" && $status != "timeout") {
	$('#cityLayer').html($response.responseText);
	}
	},
	error : function ($responseObj){
	alert("Something went wrong while processing your request.\n\nError => "
	+ $responseObj.responseText);
	}
	});
	}
	</script>
	</body>
	</html>

	//City.php
	<?php

	$conn = mysql_connect("localhost", "root", "root");
	$db = mysql_select_db("country_example", $conn);

	$country_id = $_REQUEST['country_id'];
	$sql_city = "SELECT * FROM cities WHERE country_id = '".$country_id."'";
	$result_city = mysql_query($sql_city);

	echo "<select name='city'>";
	while($row_city = mysql_fetch_array($result_city))
	{
	echo "<option value='".$row_city['id']."'>".$row_city['city']."</option>";
	}
	echo "</select>";
	?>