Get all orders for a product in WooCommerce.

example.php

<?php
/**
 * Get all orders given a product.
 *
 * @param integer $product_id The product ID.
 *
 * @return array An array of WC_Order objects.
 */
function rfm_get_orders_by_product( $product_id ) {

    global $wpdb;

    $raw = "
        SELECT
            `items`.`order_id`,
            MAX(CASE WHEN `itemmeta`.`meta_key` = '_product_id' THEN `itemmeta`.`meta_value` END) AS `product_id`
        FROM
            `{$wpdb->prefix}woocommerce_order_items` AS `items`
        INNER JOIN
            `{$wpdb->prefix}woocommerce_order_itemmeta` AS `itemmeta`
        ON
            `items`.`order_item_id` = `itemmeta`.`order_item_id`
        WHERE
            `items`.`order_item_type` IN('line_item')
        AND
            `itemmeta`.`meta_key` IN('_product_id')
        GROUP BY
            `items`.`order_item_id`
        HAVING
            `product_id` = %d";

    $sql = $wpdb->prepare( $raw, $product_id );

    return array_map(function ($data) {
        return wc_get_order( $data->order_id );
    }, $wpdb->get_results( $sql ) );

}