Dependent drop down list

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Javascript

PHP

I tried to make a simple dependent drop down list and here is the table

|

id

|

pid

|

category

|

|

1

|

0

|

animal

|

|

2

|

0

|

fruit

|

|

3

|

1

|

rabbit

|

|

4

|

2

|

lemon

|

php code for drop down list level 1:

<select name="level1" class="level1" onChange="get_level2(this.value)">
        <option selected="selected">--level 1--</option>
        <?php
        $sql_level1 = "SELECT * FROM table WHERE pid=0";
        $result_level1 = mysql_query($sql_level1);

        while($row_level1 = mysql_fetch_array($result_level1))
        {
            echo "<option value='".$row_level1['id']."'>".$row_level1['kategori']."</option>";
        }
        ?>
        </select>

The level 1 drop down work fine, but I down know how to parsing the chosen id in level 1 to make drop down level 2 based on the pid value..

How to make the level 1 selected id become level 2 pid when level 1 onChange in javascript??

Still googling but still don't solved my problem...

if i try to parsing the id to another file like this, is it correct??
function get_level2(id)
{
$.ajax({
type: "POST",
url: "../include/level2.php", /* The fruit or animal id will be sent to this file */
beforeSend: function () {
$("#level2").html("<option>Loading ...</option>");
},
data: "level2_id="+id,
success: function(msg){
$("#level2").html(msg);
}
});
}

and this is the level2.php file:

<?php
include "../include/sqlConnect.php";

$level2_id = $_REQUEST['level2_id'];

$sql_level2 = "SELECT * FROM table WHERE pid = '".$level2_id."'";
$result_level2 = mysql_query($sql_level2);
echo "<select name='level2'>";

while($row_level2 = mysql_fetch_array($result_level2))
{
echo "<option value='".$row_level2['id']."'>".$row_level2['kategori']."</option>";
}

echo "</select>";
?>

Can anyone help me please..