How to check if an inserted value exist in my database table

Hi there,

In my registration page I put a radio button to check the user_role and a text box to insert a user reference(I already have a table of references in my database type of variable varchar)

I added some code to verify that the inserted value exist in my table:

$reference_info = $_POST['reference_info'];
 $role_info = $_POST['role_info'];

        // Get All references from database
global $wpdb;
$q = "select reference from ".$wpdb->prefix."university_attributes WHERE reference ='". $reference_info. "'";
$r = $wpdb->get_results($q);
if (($role_info=='Seller') && (!in_array($reference_info,$r))){
$errors->add('reference_info', __('<strong>ERROR</strong>: Your reference information is invalid.'));
        }

But even when I put the same value stored in my table I get the error message:

Your reference information is invalid

Any help will be appreciated and thanks in advance!