Athena queries return no results on parquet tables

If you're unable to see results from Athena queries on Parquet tables, there could be several reasons. Here are a few common ones and how to address them:

• Crawler Configuration: Ensure that the AWS Glue Crawler is properly configured and has successfully cataloged the correct schema for the Parquet files. Also, the tables created by the crawler should accurately represent your Parquet files structure.

• Data Partitions: If your data in S3 is partitioned, and those partitions are not registered with Athena, it will not be able to query those partitions. You may need to run the MSCK REPAIR TABLE table_name command in Athena to load those partitions.

• Table Location: Ensure the table location in the Athena catalog matches the actual location of the Parquet files in your S3 bucket.

• S3 Permissions: Ensure that your Athena service has the correct permissions to access your S3 data.

• Data Consistency: Sometimes, due to eventual consistency in S3, there might be a delay in availability of the data.

• Parquet File Format: Ensure that Parquet files were correctly generated and do not have any corruption. You can use a tool like parquet-tools to inspect the contents of your Parquet files and ensure they contain the expected data.

• Column Names: Parquet is case-sensitive. Ensure the column names match the exact casing when querying.

In the absence of specific error messages, it can be hard to pinpoint the exact issue. Start with these common causes and if you're still having trouble, you may want to enable Athena query error logs for more insight into the problem.