Why this happens

A plugin or theme is sending a malformed query directly to your database - often because it wasn't updated for a newer version of WordPress or MySQL/MariaDB, or because custom code contains a mistake in raw SQL. Since this touches your actual data, it's one of the more delicate errors to fix.

Step-by-step fix

  1. Check the error message for which query or plugin is mentioned.
  2. Update that plugin - if no update is available, disable it temporarily.
  3. Back up your database first (this step is very important).
  4. If you can't fix it yourself, get help from a database expert or developer - mishandling the database can corrupt your site's data.

How to prevent it happening again