Make checkboxes choose content to present from a database - php

Question

I'm creating a website where the user is supposed to check a couple of checkboxes and then the site will present the data in a table.
I have been looking at this "guide", but cant make it work on my page. I get no results on my index.php, and the submit.php just shows "Array[]"
This is what I have so far:
Index.php holds the checkboxes and the jQuery script.
Checkboxes is in a drop down menu, like this:
<div id="menu">
<div id="mainmenu">Gender</div>
<div id="submenu1" style="display:none">
<div id="submenu"><a href="#">
<input type="checkbox" name="gender" value="male">Male</a></div>
<div id="submenu"><a href="#">
<input type="checkbox" name="gender" value="female">Female</a></div>
</div>
<div id="mainmenu">Price range</div>
<div id="submenu2" style="display:none">
<div id="submenu"><a href="#">
<input type="checkbox" name="price_range" value="200">200-299$</a></div>
<div id="submenu"><a href="#">
<input type="checkbox" name="price_range" value="300">300-399$</a></div>
<div id="submenu"><a href="#">
<input type="checkbox" name="price_range" value="400">400-499$</a></div>
</div>
jQuery script:
<script src="http://code.jquery.com/jquery-latest.js"></script>
<script>
function makeTable(data){
console.log(data);
var tbl_body = "";
$.each(data, function() {
var tbl_row = "";
$.each(this, function(k , v) {
tbl_row += "<td>"+v+"</td>";
})
tbl_body += "<tr>"+tbl_row+"</tr>";
})
return tbl_body;
}
function getSnowboardFilterOptions(){
var opts = [];
$checkboxes.each(function(){
if(this.checked){
opts.push(this.id);
}
});
return opts;
}
function updateSnowboards(opts){
$.ajax({
type: "POST",
url: "submit.php",
dataType : 'json',
cache: false,
data: {filterOpts: opts},
success: function(records){
$('#boards tbody').html(makeTable(records));
}
});
}
var $checkboxes = $("input:checkbox");
$checkboxes.on("change", function(){
var opts = getSnowboardFilterOptions();
updateSnowboards(opts);
});
checkboxes.trigger("change");
</script>
At last I have submit.php, which holds the php code for selecting the right stuff.
<?php
$pdo = new PDO('mysql:host=localhost;dbname=...', '...', '...');
$opts = $_POST['filterOpts'];
$qMarks = str_repeat('?,', count($opts) - 1) . '?';
$statement = $pdo->prepare("SELECT gender, price_range, brand, model, rocker_type, flex, size_range, image FROM snowboards)");
$statement -> execute($opts);
$results = $statement -> fetchAll(PDO::FETCH_ASSOC);
$json = json_encode($results);
echo($json);
?>
Right now the SELECT query isn't specified, because I don't know how.
If someone knows what I'm doing wrong, or have better suggestion to solve it, please tell.