Is "SET CHARACTER SET utf8" Required When Using PDO::MYSQL_ATTR_INIT_COMMAND?

In PDO-based PHP applications, it's common to encounter questions regarding the necessity of using both "SET NAMES utf8" and "SET CHARACTER SET utf8" when working with UTF-8 in MySQL. While "SET NAMES utf8" sets the client character set, results character set, and connection character set, "SET CHARACTER SET utf8" sets only the client character set and results character set, leaving the connection collation unset.

Is "SET CHARACTER SET utf8" Essential?

Using "SET CHARACTER SET utf8" after "SET NAMES utf8" effectively resets the connection character set and collation to their database defaults. This can lead to potential character loss during query processing. To ensure full UTF-8 support, it's crucial to use "SET NAMES" instead of "SET CHARACTER SET."

Understanding the Character Set Management Process

MySQL employs a multi-step encoding/transcoding procedure for queries and results:

1. Queries are treated as encoded in character_set_client.
2. Queries are transcoded from character_set_client to character_set_connection.
3. String values are transcoded from character_set_connection to the column character set for comparisons against column values.
4. The result set is encoded in character_set_results.

Consequences of an Exclusive "SET CHARACTER SET utf8"

If "SET CHARACTER SET utf8" is used alone, it may result in character loss in the following scenario:

• Suppose the database character set is "latin1" with columns defined with "utf8" character sets.
• A query contains characters in UTF-8 that cannot be represented by "latin1."
• In step 3, these characters will be lost during transcoding from "utf8" to "latin1," leading to query failure.

Conclusion

While it's tempting to rely solely on "SET CHARACTER SET utf8," using "SET NAMES" ensures comprehensive UTF-8 handling by properly setting the client character set, results character set, and connection character set. Setting appropriate MySQL server variables eliminates the need for these queries on every connection, optimizing performance.