The Problem

While working on your MySQL server, you might come across this error in your error log:

Error:
Incorrect definition of table mysql.column_stats: expected column 'min_value' at position 3 to have type varbinary(255), found type varchar(255).
Incorrect definition of table mysql.column_stats: expected column 'max_value' at position 4 to have type varbinary(255), found type varchar(255).

This error usually shows up after an upgrade or misconfiguration and indicates that MySQL’s internal system table mysql.column_stats has incorrect column types.

Root Cause

The columns min_value and max_value in the mysql.column_stats table are expected to have the type:

varbinary(255)

But due to an unexpected change (often during manual migration or import), they are set to:

varchar(255)

These fields store binary data (like histogram stats), so having them as varchar is not valid for MySQL’s internal use.

How to Fix It Manually via phpMyAdmin

1. Login to phpMyAdmin
   Go to your MySQL instance and navigate to the mysql database.
2. Open the column_stats Table
   Go to the Structure tab.
3. Locate the Problematic Columns
   • min_value (currently varchar(255))
   • max_value (currently varchar(255))
4. Click “Change” on Each Column
   • Change Type from varchar(255) to varbinary(255)
   • Keep all other settings the same (Null allowed, no default value)
5. Save the Changes

Final Result

Once corrected, your column types should look like this:

After saving the changes, you should no longer see the error in your MySQL error log.

Restart MySQL and Run Upgrade

To make sure everything is fully synchronized:

sudo systemctl restart mysql
sudo mysql_upgrade -u root -p

This ensures that MySQL validates all system tables and updates metadata if needed.

Verify It’s Fixed

Run this SQL command to confirm that column_stats is valid:

CHECK TABLE mysql.column_stats;