Title: Cannot add foreign key constraint database errors Last modified: November 4, 2018 --- # Cannot add foreign key constraint database errors * Resolved [Ambyomoron](https://wordpress.org/support/users/josiah-s-carberry/) * (@josiah-s-carberry) * [7 years, 7 months ago](https://wordpress.org/support/topic/cannot-add-foreign-key-constraint-database-errors/) * Using ver. 2.2.1 of plugin. * In the course of enabling maintenance mode a series of errors were logged in the web server error log. As I saw no errors in the backend itself I do not know exactly what triggered it. However, this is what I do: 1. Under Modules | Start date I click on Now, then Done 2. I set the countdown to 1 minute 3. I click on Save settings 4. Under General | Status I click on Activated 5. I click on Save settings 6. About 1 minute later Under General | Status I click on Deactivated 7. I click on Save settings * By the IP address in the errors, it is clear that they are related to the above actions. * 10:47:14.771491 stderr: PHP message: WordPress database error Cannot add foreign key constraint for query , referer: [https://mysite.com/wp-admin/options-general.php?page=wp-maintenance-mode](https://mysite.com/wp-admin/options-general.php?page=wp-maintenance-mode) * 10:47:14.771599 stderr: \t\t\t\t\tALTER TABLE `cccwp_wc_download_log`, referer: [https://mysite.com/wp-admin/options-general.php?page=wp-maintenance-mode](https://mysite.com/wp-admin/options-general.php?page=wp-maintenance-mode) * 10:47:14.771604 stderr: \t\t\t\t\tADD CONSTRAINT `fk_wc_download_log_permission_id`, referer: [https://mysite.com/wp-admin/options-general.php?page=wp-maintenance-mode](https://mysite.com/wp-admin/options-general.php?page=wp-maintenance-mode) * 10:47:14.771609 stderr: \t\t\t\t\tREFERENCES `cccwp_woocommerce_downloadable_product_permissions`(` permission_id`) ON DELETE CASCADE;, referer: [https://mysite.com/wp-admin/options-general.php?page=wp-maintenance-mode](https://mysite.com/wp-admin/options-general.php?page=wp-maintenance-mode) * 10:47:14.771612 stderr: \t\t\t\t made by require_once(‘wp-admin/admin.php’), require_once(‘wp-load.php’), require_once(‘blahblah/wp-config.php’), require_once(‘ wp-settings.php’), do_action(‘init’), WP_Hook->do_action, WP_Hook->apply_filters, WC_Install::check_version, WC_Install::install, WC_Install::create_tables, referer: [https://mysite.com/wp-admin/options-general.php?page=wp-maintenance-mode](https://mysite.com/wp-admin/options-general.php?page=wp-maintenance-mode) * I note further the following two entries in the web server access log, that may or may not be related: * From the web server: POST /wp-admin/admin-ajax.php?action=wp_1_wc_privacy_cleanup& nonce=925520a95c HTTP/1.1 * From the admin client (same as the errors above): POST /?wc-ajax=get_refreshed_fragments HTTP/2.0 Viewing 5 replies - 1 through 5 (of 5 total) * [George J](https://wordpress.org/support/users/georgejipa/) * (@georgejipa) * [7 years, 7 months ago](https://wordpress.org/support/topic/cannot-add-foreign-key-constraint-database-errors/#post-10846832) * Hello [@josiah-s-carberry](https://wordpress.org/support/users/josiah-s-carberry/), * All that errors are related to Woocommerce. I suggest opening a ticket on their support forum: [https://wordpress.org/support/plugin/woocommerce](https://wordpress.org/support/plugin/woocommerce). * — George * Thread Starter [Ambyomoron](https://wordpress.org/support/users/josiah-s-carberry/) * (@josiah-s-carberry) * [7 years, 7 months ago](https://wordpress.org/support/topic/cannot-add-foreign-key-constraint-database-errors/#post-10846912) * Thank you for this feedback, George. I will be sure to raise the issue with WooCommerce. * I wonder, though, if you would be so kind as to help me understand how such an error could occur when I am on the WP Maintenance Mode settings page? * [George J](https://wordpress.org/support/users/georgejipa/) * (@georgejipa) * [7 years, 7 months ago](https://wordpress.org/support/topic/cannot-add-foreign-key-constraint-database-errors/#post-10846954) * [@josiah-s-carberry](https://wordpress.org/support/users/josiah-s-carberry/) Because Woocommerce is running (in the background) on all pages you access. Including on WP MM settings page. * [George J](https://wordpress.org/support/users/georgejipa/) * (@georgejipa) * [7 years, 7 months ago](https://wordpress.org/support/topic/cannot-add-foreign-key-constraint-database-errors/#post-10857984) * [@josiah-s-carberry](https://wordpress.org/support/users/josiah-s-carberry/) As far as I see, your problem is solved. So, please set the status to **Resolved**. * [https://wordpress.org/support/topic/error-during-alter-table-wp_wc_download_log/](https://wordpress.org/support/topic/error-during-alter-table-wp_wc_download_log/) * Thread Starter [Ambyomoron](https://wordpress.org/support/users/josiah-s-carberry/) * (@josiah-s-carberry) * [7 years, 7 months ago](https://wordpress.org/support/topic/cannot-add-foreign-key-constraint-database-errors/#post-10858003) * It had to do with an upgrade, where changes to the database were done in the background. I suppose I was turning off maintenance mode when the error occurred, thus the reference to this plugin. Viewing 5 replies - 1 through 5 (of 5 total) The topic ‘Cannot add foreign key constraint database errors’ is closed to new replies. * ![](https://ps.w.org/wp-maintenance-mode/assets/icon-256x256.gif?rev=3027645) * [LightStart - Maintenance Mode, Coming Soon and Landing Page Builder](https://wordpress.org/plugins/wp-maintenance-mode/) * [Frequently Asked Questions](https://wordpress.org/plugins/wp-maintenance-mode/#faq) * [Support Threads](https://wordpress.org/support/plugin/wp-maintenance-mode/) * [Active Topics](https://wordpress.org/support/plugin/wp-maintenance-mode/active/) * [Unresolved Topics](https://wordpress.org/support/plugin/wp-maintenance-mode/unresolved/) * [Reviews](https://wordpress.org/support/plugin/wp-maintenance-mode/reviews/) * 5 replies * 2 participants * Last reply from: [Ambyomoron](https://wordpress.org/support/users/josiah-s-carberry/) * Last activity: [7 years, 7 months ago](https://wordpress.org/support/topic/cannot-add-foreign-key-constraint-database-errors/#post-10858003) * Status: resolved