Check out example codes for "woocommerce show out of stock products last". It will help you in understanding the concepts better.

Code Example 1

/**
* Sorting out of stock WooCommerce products - Order product collections by stock status, in-stock products first.
*/
class iWC_Orderby_Stock_Status
{
public function __construct()
{
// Check if WooCommerce is active
if (in_array('woocommerce/woocommerce.php', apply_filters('active_plugins', get_option('active_plugins')))) {
add_filter('posts_clauses', array($this, 'order_by_stock_status'), 2000);
}
}
public function order_by_stock_status($posts_clauses)
{
global $wpdb;
// only change query on WooCommerce loops
if (is_woocommerce() && (is_shop() || is_product_category() || is_product_tag())) {
$posts_clauses['join'] .= " INNER JOIN $wpdb->postmeta istockstatus ON ($wpdb->posts.ID = istockstatus.post_id) ";
$posts_clauses['orderby'] = " istockstatus.meta_value ASC, " . $posts_clauses['orderby'];
$posts_clauses['where'] = " AND istockstatus.meta_key = '_stock_status' AND istockstatus.meta_value <> '' " . $posts_clauses['where'];
}
return $posts_clauses;
}
}
new iWC_Orderby_Stock_Status;
/**
* END - Order product collections by stock status, instock products first.
*/

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