Sortable Custom Column?

I'm sorry, I speak a little English.

My MySQL table:

CREATE TABLE wp_visitors (

    `id` INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
    `post_id` INT NOT NULL

);

The ~/wp-content/themes/mycustomtheme/functions.php file:

Add a custom column:

function add_sticky_column ( $columns ) {

    return array_merge ( $columns, array ( 'sticky'= 'Visitors' ) );

}

add_filter ( 'manage_posts_columns' , 'add_sticky_column' );

The Visitors custom column values:

function display_posts_stickiness ( $column, $post_id ) {

    if ( $column == 'sticky' ) {

        echo custom_counter ( $post_id );

    } else {}

}

add_action ( 'manage_posts_custom_column' , 'display_posts_stickiness', 10, 2 );

The custom_counter function:

function custom_counter ( $post_id ) {

    global $wpdb;

    $prefix = $wpdb- prefix; // wp_

    $mysqli = new mysqli ( DB_HOST, DB_USER, DB_PASSWORD, DB_NAME );

    $sql = SELECT * FROM ` . $prefix . visitors` WHERE `post_id`= . $post_id;

    $result = $mysqli- query ( $sql );

    $row_cnt = $result- num_rows;

    $mysqli- close ();

    return $row_cnt;

}

Sorting:

function ws_sortable_manufacturer_column ( $columns ) {

    $columns [ 'sticky' ] = 'Visitors';

    return $columns;

}

add_filter ( 'manage_edit-post_sortable_columns', 'ws_sortable_manufacturer_column' );

It works! Need help for:

function ws_orderby_custom_column ( $query ) {

    global $pagenow;

    if ( ! is_admin () || 'edit.php' != $pagenow || ! $query- is_main_query () || 'post' != $query- get ( 'post_type' ) ) {

        return;

    } else {}

    $orderby = $query- get ( 'orderby' );

    switch ( $orderby ) {

        case 'Visitors':

            // please help me!

            break;

        default:

            break;

    }

}

add_action ( 'pre_get_posts', 'ws_orderby_custom_column' );

Please help me. Thanks.