Come creare una pagina con due select correlate fra di loro

<?php
/**
* Template Name: GrandPrix Template
*
* Description: A Page Template that adds a sidebar to pages.
*
* @package WordPress
* @subpackage Twenty_Eleven
* @since Twenty Eleven 1.0
*/

get_header();

global $wpdb;

// carica tutte le gare
$gare_2016 = $wpdb->get_results(“SELECT id,nome,luogo,data FROM “.$wpdb->prefix.”gpaltvt_gare WHERE data like ‘2016%’ order
by data”);
$gare_2017 = $wpdb->get_results(“SELECT id,nome,luogo,data FROM “.$wpdb->prefix.”gpaltvt_gare WHERE data like ‘2017%’ order
by data”);

$anni = $wpdb->get_results(“SELECT DISTINCT(date_format(data, ‘%Y’)) AS id FROM “.$wpdb->prefix.”gpaltvt_gare order by id”
);
echo “<script>”;
echo ”    function populate(s1,s2){“;
echo ”    var s1 = document.getElementById(s1);”;
echo ”    var s2 = document.getElementById(s2);”;
echo ‘    s2.innerHTML = “”; ‘;
echo ”    alert(‘prova’);”;
echo ”    if(s1.value == 2016 ){“;
echo ”    var optionArray = [“;
foreach ( $gare_2016 as $gara ) {
echo chr(34);echo $gara->id;echo chr(124);echo $gara->nome; echo chr(34);
}
echo ”    } else if(s1.value == 2017 ){“;
echo ”    var optionArray = [“;
foreach ( $gare_2017 as $gara ) {
echo chr(34);echo $gara->id;echo chr(124);echo $gara->nome;echo chr(34);echo chr(44);
}
echo ”    }”;
echo ”    for(var option in optionArray){ “;
echo ‘    var pair = optionArray[option].split(“|”); ‘;
echo ‘    var newOption = document.createElement(“option”); ‘;
echo ”    newOption.value = pair[0]; “;
echo ”    newOption.innerHTML = pair[1]; “;
echo ”    s2.options.add(newOption); “;
echo ”    }”;
echo ”    }”;
echo “</script>”;
echo ” <div id=\”primary\”> “;
echo ” <div id=\”content\” role=\”main\”> “;
echo ”    <h2>Visualizza Classifica. Anno: “;
echo ”    <select id=slct1 name=slct1 onchange=populate(this.id,’slct2’)> “;
echo ‘    <option value=””></option> ‘;
foreach ($anni as $anno)
{
$year=$anno->id;
// “<option value=”.$year.”>”.$year.”</option> ” ;
$optionh=”<option value=”;
$optionm=”>”;
$optiont=”</option>”;
$option=$optionh.$year.$optionm.$year.$optiont ;
echo “$option”;
}
echo “</select>”;
echo “Gara:”;
echo “<select id=slct2 name=slct2></select>”;
echo “<hr />”;
echo ”    </div><!– #content –>”;
echo ”    </div><!– #primary –>”;
get_footer();
?>