Add index for query optimization

upgrade/upgrade_module_2_1_0.php

@@ -0,0 +1,29 @@
+<?php
+/**
+ * Copyright since 2007 PrestaShop SA and Contributors
+ * PrestaShop is an International Registered Trademark & Property of PrestaShop SA
+ *
+ * NOTICE OF LICENSE
+ *
+ * This source file is subject to the Academic Free License 3.0 (AFL-3.0)
+ * that is bundled with this package in the file LICENSE.md.
+ * It is also available through the world-wide-web at this URL:
+ * https://opensource.org/licenses/AFL-3.0
+ * If you did not receive a copy of the license and are unable to
+ * obtain it through the world-wide-web, please send an email
+ * to license@prestashop.com so we can send you a copy immediately.
+ *
+ * DISCLAIMER
+ *
+ * Do not edit or add to this file if you wish to upgrade PrestaShop to newer
+ * versions in the future. If you wish to customize PrestaShop for your
+ * needs please refer to https://devdocs.prestashop.com/ for more information.
+ *
+ * @author    PrestaShop SA and Contributors <contact@prestashop.com>
+ * @copyright Since 2007 PrestaShop SA and Contributors
+ * @license   https://opensource.org/licenses/AFL-3.0 Academic Free License 3.0 (AFL-3.0)
+ */
+function upgrade_module_2_1_0($module)
+{
+    return Db::getInstance()->execute('ALTER TABLE `' . _DB_PREFIX_ . '_order_detail` ADD INDEX `product_shop` (`product_id`, `id_shop`);');
+}