How to Solve Unknown Collation: utf8mb4_0900_ai_ci Error

Recent MySQL users who encountered the Unknown collation: ‘utf8mb4_0900_ai_ci’ error when working with the database system have met similar issues. The problem occurs because databases have different character sets and collation configurations. The following post examines MySQL collation as an error mechanism, along with the causes along with necessary solutions.

What is Collation in MySQL?

MySQL explains that “A collation represents the set of rules that specifies string character comparison and sorting sequences.” A MySQL data collation remains restricted to operating within one character set boundary. The territory of character sets extends to a minimum collation, but standard character sets typically come with two or multiple collations.

Collations define:

• Character sets: The storage encoding of characters for the database falls under the category of character sets, and utf8mb4 represents one such set. (e.g., utf8mb4).
• Sorting rules: Character comparison and sort rules define the process for sorting characters against each other.
• Case and accent sensitivity: The collation system contains two elements: case and accent sensitivity status.

For example, the collation utf8mb4_0900_ai_ci can be broken down as:

• utf8mb4: A 4-byte UTF-8 Unicode encoding character set.
• 0900: The Unicode Collation Algorithm (UCA) version.
• ai: Accent-insensitive.
• ci: Case-insensitive.

Why Does the Error Occur?

You will encounter the “Unknown collation” error when using MySQL 5.7 or earlier versions that cannot support the MySQL 8.x introduced collations. MySQL version 5.7 and older will not identify the utf8mb4_0900_ai_ci collation when you attempt database import or restoration operations. Consequently, the system generates an error.

How to Fix the Error

Several solutions exist to handle the problem as follows:

1. Upgrade MySQL

Upgrading your MySQL server to the version that supports ‘utf8mb4_0900_ai_ci’ (MySQL 8.x) represents the recommended remedy. The simplest solution to resolve the issue occurs when new collations become compatible with your system.

2. Change Collation Before Export

 If upgrading is not an option, adjust the collation in your source database before exporting:

ALTER TABLE tableName
CONVERT TO CHARACTER SET utf8mb4
COLLATE utf8mb4_general_ci;

Then, export the database again. This will ensure that the exported SQL file does not contain the unrecognized collation.

3. SED Command on Dump File
   If you already have a dump file referencing utf8mb4_0900_ai_ci, you can replace that collation in the file using a text editor or a sed command in Linux:

sed -i 's/utf8mb4_0900_ai_ci/utf8mb4_general_ci/g' your_dump_file.sql

After this, import the modified dump file into the older MySQL instance.

4. Specify Default Collation for Database

When creating or restoring the database, explicitly set a default character set and collation that your MySQL version supports:

CREATE DATABASE yourDatabaseName
DEFAULT CHARACTER SET utf8mb4
DEFAULT COLLATE utf8mb4_general_ci;

This ensures MySQL doesn’t try to use collations unsupported by your server version.

Conclusion

A mismatch between MySQL versions or the use of unsupported default collations usually triggers this Unknown collation: ‘utf8mb4_0900_ai_ci’ error. Upgrading your MySQL instance or modifying collation settings in your database eliminates the Unknown collation: ‘utf8mb4_0900_ai_ci’ error. The selection of supported collations in SQL dumps during backup procedures enables MySQL environments to maintain a consistent connection.

All MySQL servers must be up to date, and your databases must use collations which the target MySQL version supports. Database migrations will proceed smoothly because this measure prevents compatibility issues.

Further Reading

• MySQL 8.0 Reference Manual on Character Sets and Collations
• Collation and Character Set Concepts

Feel free to reach out if you have any questions or run into issues with your MySQL environment.