Resolving Common YITH WooCommerce Wishlist Database Errors

Many users of the YITH WooCommerce Wishlist plugin encounter database-related errors that can prevent the wishlist from functioning correctly. These errors often manifest as SQL syntax issues or missing database tables, causing buttons to stop working or error messages to appear on product pages. Based on community reports and solutions, this guide outlines the most common causes and their fixes.

Common Error 1: SQL Syntax Error Near ')'

Symptoms: Errors in your server logs containing phrases like "You have an error in your SQL syntax... near ')'". The wishlist button may become unresponsive, or fragments may fail to load.

Cause: This is a known bug that can occur in certain versions of the plugin where a SQL query is generated with an empty NOT IN () clause.

Solution: Add the following code to your active child theme's functions.php file. This filter disables the problematic part of the query.

add_filter( 'yith_wcwl_remove_hidden_products_via_query', '__return_false' );

This is a widely confirmed workaround from the community. The YITH WooCommerce Wishlist team has been made aware of this issue for a future update.

Common Error 2: Missing Database Tables

Symptoms: Errors stating that a table doesn't exist, such as Table '...wp_yith_wcwl_lists' doesn't exist. This often happens after a migration, update, or on a fresh installation.

Cause: The plugin's database tables were not created correctly or were corrupted during an update.

Solution: Force the plugin to recreate its database tables by following these steps:

1. Navigate to your WordPress admin dashboard.
2. Go to yoursite.com/wp-admin/options.php.
3. On the options page, use your browser's search function (Ctrl+F or Cmd+F).
4. Search for the option: yith_wcwl_db_version.
5. Delete the value in its text field, leaving it completely empty.
6. Scroll to the bottom of the page and click 'Save Changes'.
7. Deactivate and then reactivate the YITH WooCommerce Wishlist plugin.

This process triggers the plugin's table installation routine again.

Common Error 3: Unknown Character Set 'utf8mb4_general_ci'

Symptoms: Errors during table creation that reference an unknown character set, preventing the plugin from installing correctly.

Cause: This typically occurs on older MySQL server versions that do not support the utf8mb4 character set and its collations.

Solution: The most effective solution is to contact your hosting provider and request that they update your MySQL server to a more recent version (MySQL 5.5.3 or later) that supports utf8mb4. This is a server-level requirement for many modern plugins.

General Troubleshooting Steps

If the errors persist after trying the solutions above, perform a general conflict test:

1. Switch temporarily to a default WordPress theme (like Twenty Twenty-Four).
2. Deactivate all plugins except for WooCommerce and YITH WooCommerce Wishlist.
3. Check if the issue is resolved.
4. If it is, reactivate your theme and plugins one by one to identify the source of the conflict.

Always remember to clear any caching on your site (server, plugin, or CDN) and in your browser after making these changes.