Problem with autocomplete.

Problem with autocomplete.

Hi everybody,
I have a problem with autocomplete.
 The source data are stored in database.
Ajax calls citta.php, that should give the name of the town when I start writing.

<script>
$( "#campo" ).autocomplete({
    minLength: 2,
    source: "citta.php"    
});
</script>

Instead if I use an array where I write some towns it works good.

citta.php:

$return_arr = array();
  
 include("../Registrazione/config.php"); //connect to database

    if (isset($_GET) && isset($_GET['term']) && !empty($_GET['term'])) {
        $term = $_GET['term'];
      
        $query = "SELECT * FROM comuni WHERE comune LIKE '%{$term}%' ORDER BY comune ASC";
        $fetch = mysql_query($query);
      
        while ($row = mysql_fetch_array($fetch, MYSQL_ASSOC)) {
            $row_array['label'] = $row['comune'];
            $row_array['value'] = $row['id_com'];
            array_push($return_arr, $row_array);
        }
    }

echo json_encode($return_arr);

Please, can someone helps me?

Thanks in advance.

Tegatti