/**
 * 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;
}