How to populate a child drop down menu from parent selection PHP - php

Question

How would one populate a child drop down selection on a static page from a parent drop down using only PHP. E.g having a child drop down populate with counties after you have selected which state you live in, or in my case populate series after manufacturer.
EDIT: Is there a way to do it without js?
<?php
$man = mysqli_query($con,"SELECT DISTINCT manufacturer FROM inventory.manufacturer WHERE manufacturer!=\"\" ORDER BY manufacturer;");
echo "<select name=\"manufacturerS\">
<option value=\"\">Select</option>";
while($row = mysqli_fetch_array($man)) {
echo "<option value=\"".$row['manufacturer']."\">".$row['manufacturer']."</option>";
}
echo "</td>
<td>";
if(isset($_POST['manufacturerS'])){
$ser = mysqli_query($con,"SELECT DISTINCT series, manufacturer FROM inventory.audit WHERE series!=\"\" AND manufacturer='".$_POST['manufacturerS']."' ORDER BY series;");
echo "<select name=\"seriesS\">
<option value=\"\">Select</option>";
while($row = mysqli_fetch_array($ser)) {
echo "<option value=\"".$row['series']."\">".$row['series']."</option>";
}
echo "</td>
<td>";
}

Answer 1

You need of client-side to determine when manufacturerS select was selected, then you can use pure javascript:
<form id="manufacturerF" method="POST">
<select name="manufacturerS" onchange="document.getElementById('manufacturerF').submit();">
<?php
$man = mysqli_query($con, "SELECT DISTINCT manufacturer
FROM inventory.manufacturer
WHERE manufacturer!=\"\"
ORDER BY manufacturer;");
while ($row = mysqli_fetch_array($man)) {
echo '<option value="'.$row['manufacturer'].'>'.$row['manufacturer'].'</option>';
}
?>
</select>
</form>
<?php
if(isset($_POST['manufacturerS']) && !empty($_POST['manufacturerS'])){
echo '<select name="seriesS">';
$ser = mysqli_query($con,"SELECT DISTINCT series, manufacturer
FROM inventory.audit
WHERE series!=\"\"
AND manufacturer='".$_POST['manufacturerS']."'
ORDER BY series;");
while ($row = mysqli_fetch_array($ser)) {
echo '<option value="'.$row['series'].'">'.$row['series'].'</option>';
}
echo '</select>';
}
?>
I recommend you use JQuery so will not need a <form> and reload your page.
The correct idea would be to use JQUERY to detect when the select1 was selected and then with AJAX populate the select2