## Does \'SET CHARACTER SET utf8\' Have Real Value in MySQL Connections?

Does "SET CHARACTER SET utf8" Command Hold Significance?

When working with MySQL and UTF-8 in PHP, it has been customary to utilize both "SET NAMES utf8" and "SET CHARACTER SET utf8" commands. However, when using PDO's PDO::MYSQL_ATTR_INIT_COMMAND parameter, only a single query is supported. This raises the question: is "SET CHARACTER SET utf8" necessary at all?

Delving into the Technicalities

The "SET NAMES utf8" command sets various MySQL character set-related system variables:

• character_set_client
• character_set_results
• character_set_connection

On the other hand, "SET CHARACTER SET utf8" affects only two variables:

• character_set_client
• character_set_results

Critically, "SET CHARACTER SET utf8" also resets the character_set_connection and collation_connection variables to their database-level defaults.

Understanding the MySQL Encoding/Transcoding Process

MySQL undergoes a multi-step encoding/transcoding process for both incoming queries and result sets:

1. Queries are initially treated as being encoded in character_set_client.
2. Queries are transcoded from character_set_client into character_set_connection.
3. String values for comparison are transcoded from character_set_connection into the column's character set.
4. Result sets are generated in character_set_results.

The Case for "SET NAMES ...": Avoiding Data Loss

Since "SET CHARACTER SET utf8" resets character_set_connection to the database default, this can potentially lead to data loss, especially if the database default is not UTF-8. This is because the transcoding process in step 3 may result in UTF-8 characters being lost if the database default cannot represent them.

Conclusion

While setting up MySQL server variables correctly avoids the performance overhead of an extra query on each connection, it is generally advisable to use "SET NAMES ..." to ensure proper character set support. This command sets all necessary variables and prevents potential data loss scenarios, guaranteeing a robust UTF-8 environment.

The above is the detailed content of ## Does \'SET CHARACTER SET utf8\' Have Real Value in MySQL Connections?. For more information, please follow other related articles on the PHP Chinese website!