Athena MySQL Connector adding unexpected partition field

The unexpected "partition_name" column you're seeing in your Athena query results when using the MySQL connector is actually a normal behavior of the connector. This synthetic column is created by Athena to help with query optimization and data retrieval, even if you don't have any partitions set up in your RDS MySQL table.

The Athena MySQL connector uses this synthetic partition column to determine how to generate splits for the connector. It's important to note that this column is not actually modifying your table definition in RDS; it's only used internally by Athena to improve query performance.

The "partition_name" column with all values set to "*" is essentially a placeholder that allows Athena to use its internal partitioning mechanism even when the source MySQL table isn't partitioned. This approach helps Athena to potentially parallelize queries and improve overall performance when working with federated data sources.

You don't need to take any action regarding this column, as it's part of how the Athena MySQL connector operates. It doesn't affect your actual data or table structure in RDS. If you need to work with your data without this additional column, you can simply exclude it from your SELECT statements in your Athena queries.
Sources
Amazon Athena MySQL connector - Amazon Athena