WP_User_Query with sorting, filtering and pagination

    global $wpdb;

    $show = (isset($_GET['show'])) ? $_GET['show'] : 'all';
    $sort_by = (isset($_GET['sort'])) ? $_GET['sort'] : 'login';
    $sort_order = (isset($_GET['order'])) ? $_GET['order'] : 'ASC';
    $num_posts = (isset($_GET['num'])) ? $_GET['num'] : 20;
    $user = (isset($_POST['user'])) ? $_POST['user'] : 'all';
    $paged = (isset($_GET['paged'])) ? $_GET['paged'] : 1;

    // If a specific user, reset all other params to defaults (only 1 record to show).
    if ($user != 'all') {
        $show = 'all';
        $sort_by = 'login';
        $sort_order = 'ASC';
        $paged = 1;
    }

    $user_clause = ($user == 'all') ? "" : "AND a.ID = " . $user;
    $role_clause = ($show == 'all') ? "" : "AND b.meta_key = 'aa_capabilities' AND b.meta_value LIKE '%" . $show . "%'";
    switch ($sort_by) {
        case 'login':
            $sort_clause = "ORDER BY LOWER(a.user_login) " . $sort_order;
            break;
        case 'email':
            $sort_clause = "ORDER BY LOWER(a.user_email) " . $sort_order;
            break;
        case 'display_name':
            $sort_clause = "ORDER BY LOWER(a.display_name) " . $sort_order;
            break;
        case 'balance':
            $sort_clause = "ORDER BY CAST(c.meta_value AS decimal) " . $sort_order;
            break;
        default:
            $sort_clause = "ORDER BY LOWER(a.user_login) " . $sort_order;
            break;
    }

    $query =   "SELECT COUNT(DISTINCT a.ID) FROM $wpdb->users a
                JOIN $wpdb->usermeta b ON a.ID = b.user_id
                JOIN $wpdb->usermeta c ON a.ID = c.user_id
                WHERE c.meta_key = '_account_balance'
                " . $user_clause . " " . $role_clause . " " . $sort_clause;

    $num_users = $wpdb->get_var($query);

    // Work out pagination.
    $num_pages = ceil($num_users/$num_posts);
    $bottom_limit = $num_posts*($paged-1);

    $limit_clause = "LIMIT " . $num_posts . " OFFSET " . (($bottom_limit>0) ? $bottom_limit : 0);

    // Get actual results.
    $query =   "SELECT DISTINCT a.ID FROM $wpdb->users a
                JOIN $wpdb->usermeta b ON a.ID = b.user_id
                JOIN $wpdb->usermeta c ON a.ID = c.user_id
                WHERE c.meta_key = '_account_balance'
                " . $user_clause . " " . $role_clause . " " . $sort_clause . " " . $limit_clause;

    $userlist = $wpdb->get_results($query);

    if ($num_users > 0) {
    // Display code goes here (the foreach $userlist, yada yada yada)

    }

    if ($paged > 1) {
        $prev = $paged-1;
        echo '<span class="link-class"><a href="' . $base_url . '&show=' . $show . '&sort=' . $sort_by . '&order=' . $sort_order . '&num=' . $num_posts . '&paged=' . $prev . '">« Previous</a></span>&nbsp;&nbsp;&nbsp;';
    }
    if ($num_pages > 1 && $paged < $num_pages) {
        $next = $paged+1;
        echo  '<span class="link-class"><a href="' . $base_url . '&show=' . $show . '&sort=' . $sort_by . '&order=' . $sort_order . '&num=' . $num_posts . '&paged=' . $next . '">Next »</a></span>';
    }