The error message “Unknown collation: ‘utf8mb4_0900_ai_ci'” typically occurs in database systems like MySQL when there’s a mismatch between the collation specified for a column and the collation supported by the database server.

In MySQL, “utf8mb4_0900_ai_ci” is a collation introduced in version 8.0.1 to support the utf8mb4 character set with the 0900 (Unicode 9.0.0) sorting rules and the AI (Accent Insensitive) comparison. If you’re encountering this error, it’s likely because you’re trying to use this collation on a MySQL version that does not support it, or there’s a typo in the collation name.

Here are some steps you can take to resolve this issue:

  1. Check MySQL Version: Ensure that you’re using MySQL version 8.0.1 or newer. If you’re using an older version, you won’t have support for this collation.
  2. Verify Collation Name: Double-check the collation name in your database schema. Ensure that it’s spelled correctly and that there are no extra spaces or typos.
  3. Fallback to Compatible Collation: If your MySQL version doesn’t support “utf8mb4_0900_ai_ci,” consider using a compatible collation that is supported by your version. For example, “utf8mb4_unicode_ci” or “utf8mb4_general_ci” are widely supported collations for UTF-8 encoding.
  4. Upgrade MySQL: If possible, consider upgrading your MySQL server to a version that supports the collation you need. This may require planning and testing, especially for production environments.
  5. Character Set Configuration: Ensure that your database and table are configured to use the “utf8mb4” character set. This collation is specifically designed for the utf8mb4 character set.
  6. Database Migration: If none of the above options work for you and you must use the “utf8mb4_0900_ai_ci” collation, consider migrating your database to a MySQL server that supports it.

By following these steps, you should be able to resolve the “Unknown collation: ‘utf8mb4_0900_ai_ci'” error in MySQL.