WordPress: sort Previous and Next post by menu_order

functions-sort-prev-next-by-menu-order.php

<?php
function my_previous_post_where() {
	global $post, $wpdb;
	return $wpdb->prepare( "WHERE p.menu_order < %s AND p.post_type = %s AND p.post_status = 'publish'", $post->menu_order, $post->post_type);
}
add_filter( 'get_previous_post_where', 'my_previous_post_where' );
function my_next_post_where() {
	global $post, $wpdb;
	return $wpdb->prepare( "WHERE p.menu_order > %s AND p.post_type = %s AND p.post_status = 'publish'", $post->menu_order, $post->post_type);
}
add_filter( 'get_next_post_where', 'my_next_post_where' );
function my_previous_post_sort() {
	return "ORDER BY p.menu_order desc LIMIT 1";
}
add_filter( 'get_previous_post_sort', 'my_previous_post_sort' );
function my_next_post_sort() {
	return "ORDER BY p.menu_order asc LIMIT 1";
}
add_filter( 'get_next_post_sort', 'my_next_post_sort' );