Creating two dependent Dropdown List - php

Question

I want to make the third drop down populated based on selection on second drop down refer value from first and second drop down.
jQuery
<script type="text/javascript">
$(document).ready(function() {
$("#parent_cat").change(function() {
$.get('loadsubcat.php?parent_cat=' + $(this).val(), function(data) {
$("#sub_cat").html(data);
});
});
$("#sub_cat").change(function() {
$.get('loadsubelement.php?sub_cat=' + $(this).val() + $('#parent_cat').val(), function(data) {
$("#select_subelement").html(data);
});
});
});
</script>
loadsubelement.php
<?php
include('config.php');
$parent_cat = $_GET['parent_cat'];
$sub_cat = $_GET['sub_cat'];
$query = mysqli_query($connection, "SELECT * FROM maincategories WHERE categoryID = {$parent_cat}");
$query = mysqli_query($connection, "SELECT * FROM maincategories WHERE subcategoryID = {$sub_cat}");
echo '<option value="">Please select</option>';
while($row = mysqli_fetch_array($query)) {
echo '<option value="'.$row['subcategoryID'].'">' . $row['maincategory_name'] . "</option>";
}
?>

Answer 1

I think you have to change your query string like this:
$.get('loadsubelement.php?sub_cat=' + $(this).val() +
"&parent_cat" + $('#parent_cat').val()
You are missing this: "&parent_cat" in your second ajax call.
Or a better way of doing is to send the an object like this:
$("#sub_cat").change(function() {
var dataString = {
parent_cat : $('#parent_cat').val(),
sub_cat : $(this).val()
};
if($('#parent_cat').val() !== ""){ // check if value is selected or not i guessed default value as "".
alert("Please choose the parent value.");
$('#parent_cat').focus(); // apply focus on the element.
return false;
}else{
$.get('loadsubelement.php', dataString, function(data) {
$("#select_subelement").html(data);
});
}
});

Answer 2

jQuery(function($) {
jQuery("#office_id").change(function(){
var inputString=jQuery("#office_id").val();
$.post("?r=reports/summary/loademployees/", {office_id: ""+inputString+""}, function(data){
$('#employee_id').fadeIn();
$('#employee_id').html(data);
}
});
});
});
This is a program triggers when when u change a dropdown containing offices having id as office_id and load employees (another dropdown box having id employee_id) of that office.