Populate an associative select from a database - php

Question

Here's my problem: I have two select fields in my web application.
The second one depends on the choice made on the first one. The first one is populated from my database with the classical:
<?php
//connection to database in an include file
$query = "SELECT DISTINCT platform
FROM Appversions";
$res = mysql_query($query);
while($row = mysql_fetch_array($res)) {
echo "<option value=\"\"" . $row['platform'] . "</option>\n";
}
?>
which is working just fine.
But then I need to populate my second select with a query that would look like:
SELECT version
FROM Appversions
WHERE platform = <choice made in first select>;
I understand that I need to use JavaScript with an onChange function call to do that, but I can't figure out what that function should look like or how it will have access to my query result.

Answer 1

Usually i have this jquery code:
$('#select1').change(function(){
if($(this).val() == ''){
$('#select2').attr('disabled', 'true');
}else{
var select1 = $(this).val();
$.getJSON('index.php',
{
option: "com_spin",
controller: "guest",
task: "getProvincieByRegionId",
idRegione: idRegione
},
function(json){
$('#select2').html(json.html);
}
);
$('#select2').removeAttr('disabled');
}
});
in php i have something like this (basically i return the html for the options:
Zend_Loader::loadClass ( 'Zend_Json' );
$idRegione = JRequest::getVar ( "idRegione" );
$modelProvince = new Spin_lkpprovincia ();
$provincie = $modelProvince->getElencoProvinciePerRegione ( $idRegione );
$html = "<option value=''>Selezionare una voce</option>";
foreach ( $provincie as $provincia ) {
$html .= "<option value='" . $provincia ['idProvincia'] . "'>" . $provincia ['nome'] . "</option>";
}
$json = array (
success => "OK",
html => $html );
$json = Zend_Json::encode ( $json );
echo $json;
die ();