dependent dynamic dropdown in php - php

Question

Here I have two dependent drop downs.
First drop down is displaying all accounts(name and id).
<select name="account" id="account" class="input-name">
<?php
$query = "SELECT id,name FROM account";
$results = mysqli_query(con, $query);
while($account = $results ->fetch_assoc()){
?>
<option value="<?php echo $account["id"]; ?>"><?php echo $account["name].'-'.$account["id"];?</option>
<?php } ?>
</select>
In second drop down I need to display selected account users.
<select name="extension" id="extension" class="input-name">
<?php
$query = "SELECT ext FROM user WHERE account=100"; //Query for users for selected account.
$results = mysqli_query($con, $query);
while($user= $results ->fetch_assoc()){
?>
<option value="<?php echo $user["ext"]; ?>"><?php echo $users["ext"];?></option>
<?php } ?>
</select>
How can I filter users according to select company. Need help.

Answer 1

You may reload page after first value was selected and load page with second param. for example
<select onchange="window.location.href='some url with some value?select_value=' + this.value">...options...</select>"
Or if you do not want to reload page you can use AJAX. send request with ajax to server and replace options in second select.
with jquery
$('select.first-select').change(function(){
var value = $(this).val();
$.get('get-account', { val: value }, function(){ ...replace options... })
})

Answer 2

You can do it by using Jquery ajax request. Write an onchange method on first dropdown. On change take the id of selected account and pass it to your query for selecting users.Return all the users and display it to your users dropdown.