/**
* Get All orders IDs for a given product ID.
*
* @param integer $product_id (required)
* @param array $order_status (optional) Default is 'wc-completed'
*
* @return array
*/
function get_orders_ids_by_product_id( $product_id, $order_status = array( 'wc-completed' ) ){
global $wpdb;
$results = $wpdb->get_col("
SELECT order_items.order_id
FROM {$wpdb->prefix}woocommerce_order_items as order_items
LEFT JOIN {$wpdb->prefix}woocommerce_order_itemmeta as order_item_meta ON order_items.order_item_id = order_item_meta.order_item_id
LEFT JOIN {$wpdb->posts} AS posts ON order_items.order_id = posts.ID
WHERE posts.post_type = 'shop_order'
AND posts.post_status IN ( '" . implode( "','", $order_status ) . "' )
AND order_items.order_item_type = 'line_item'
AND order_item_meta.meta_key = '_product_id'
AND order_item_meta.meta_value = '$product_id'
");
return $results;
}