“Illegal mix of collations” Error in Your WordPress Debug Log
Short version: open a ticket and we’ll fix it. This article exists so you know what the error means and that we already have a playbook for it.
What you’re seeing
If you’ve been looking at your WordPress debug log, your Rank Math Analytics dashboard, or your hosting control panel, you may have noticed errors that look like this:
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WordPress database error: [Illegal mix of collations (utf8mb4_unicode_520_ci,IMPLICIT) and (utf8mb4_unicode_ci,IMPLICIT) for operation '='] |
It’s most commonly surfaced by Rank Math’s analytics queries, but it can also show up from WooCommerce, search plugins, membership plugins, and anything else that joins data across multiple database tables.
What it means in plain English
Your database has two or more tables that were created with slightly different text-sorting rules. MySQL refuses to compare text across tables that don’t agree on those rules, so the queries that depend on the comparison fail. The data is still there. The plugin trying to read it just can’t run the query.
This is almost always the result of a past migration, a database restore from an older server, or an older plugin that hardcoded its own collation when it created its tables. It’s not something you did wrong, and it’s not a problem with any specific plugin.
What to do
Submit a support ticket and we’ll fix it for you. This is exactly the kind of thing your managed hosting plan covers, and we’ve fixed it on enough sites to have a standard playbook:
- Full database backup before we touch anything
- Diagnostic query to identify which tables and columns are mismatched
- Standardize the whole database on a single collation in one pass
- Verify the fix and confirm the error log is clean
- Make sure your
wp-config.phpis set correctly so it doesn’t come back
Most fixes are done within a few hours of ticket submission. You don’t need to do anything beforehand.
Open a ticket
Submit a ticket here or email [email protected]. If you can paste a copy of the error message from your debug log into the ticket, that helps us confirm the variant of the issue, but it’s not required.
Want to read more?
We wrote a full technical breakdown of this error on the Glimmernet blog for the benefit of the broader WordPress community — including the SQL queries, the reasoning behind the fix, and why this error keeps happening on budget hosting. If you’re curious about the why and how, head over to the full article.
If you’re a Glimmernet customer, you don’t need to read it. Just open a ticket and we’ll handle it.
