$wpdb variable throw this error Call to a member function get_results() on a non-object in

I’ve this error “Call to a member function get_results() on a non-object in”
from this code:

require_once($_SERVER['DOCUMENT_ROOT'] . $folder . '/wp-config.php');
require_once($_SERVER['DOCUMENT_ROOT'] .  $folder . '/wp-load.php');
if (!$wpdb) {
$wpdb = new wpdb( DB_USER, DB_PASSWORD, DB_NAME, DB_HOST);
} else {
    global $wpdb;
}

function vendorDatails( $param)
{
    if ((substr ($param, 0, 0)) == '#')
    {
        substr($param, 1);
    }

    $order_ids = $wpdb->get_results( 
                                    "
                                     SELECT DISTINCT vendor_id 
                                     FROM $wpdb->lqrhxf_pv_commission 
                                     WHERE order_id = %d
                                    ",
                                        $param
                                );

    foreach ( $order_ids as $order_id )
    {
        echo $order_id->vendor_id;
    }
}

The db parameters are loaded successfully but I’ve the error on the line above when I use $wpdb variable:

 $order_ids = $wpdb->get_results( 

This is a PHP variable scope issue, there is no $wpdb defined in your function.

Add

global $wpdb;

before trying to use the $wpdb object.