Problem with $.getJSON in jquery - php

Question

My Jquery code
function nalozi() {
var id_skupine = $('#skupina option:selected').val();
$('#artikel option').remove();
//$('#artikel').append('<option value="'+id_skupine+'">'+id_skupine+'</option>');
$.getJSON('artikli.php', {id_skupine:$('#skupina').val()}, function(data) {
$.each(data, function(index,item) {
$("#artikel").append("<option value=" + item.id + ">" + item.ime_artikla + "</option>");
});
});
}
$(document).ready(function() {
nalozi();
$('#skupina').change(function() {
nalozi();
});
});
AND PHP CODE
<?php
if(isset($_GET['id_skupine']))
{
$id_skupine = $_GET['id_skupine'];
$poizvedba = mysql_query("SELECT id,ime_artikla FROM artikli WHERE id_skupine = '$id_skupine'");
$velikost = mysql_num_rows($poizvedba);
for ($i=0;$i<$velikost;$i++)
{
$elements[]=mysql_fetch_assoc($poizvedba);
}
}
echo json_encode($elements);
?>
I don't get the values back.

Answer 1

Update:
You should never put variable before sanitalizing/validating/type-converting into your sql queries. If your the value you expect in query string is a number, you need to properly type-cast it like this:
$id_skupine = (int) $_GET['id_skupine'];
And if it is a string, the least you can do is to use mysql_real_escape_string function:
$str = mysql_real_escape_string($_GET['str']);
Shouldn't you be grabbing the records from db like this:
if(isset($_GET['id_skupine']))
{
$id_skupine = $_GET['id_skupine'];
$poizvedba = mysql_query("SELECT id,ime_artikla FROM artikli WHERE id_skupine = '$id_skupine'");
$velikost = mysql_num_rows($poizvedba);
while($row = mysql_fetch_assoc($poizvedba)){
$elements[] = $row['ime_artikla'];
}
}
echo json_encode($elements);

Answer 2

Might be your query is not returning anything
$poizvedba = mysql_query("SELECT id,ime_artikla FROM artikli WHERE id_skupine = '$id_skupine'");
Remove single quote from '$id_skupine'
Try
$poizvedba = mysql_query("SELECT id,ime_artikla FROM artikli WHERE id_skupine = '".$id_skupine."'");