Athena unload lowercases all camelCase columns in parquet

Question

I am using Athena UNLOAD query to unload results of SELECT in parquet format. I have columns in snake_case in Athena Table. So I did SELECT snake_case as snakeCase .. in my query. 
The problem is I see all the Column in unload parquet files area lowercased. It seems ATHENA UNLOAD Command does not care about the case and lower case every column.

Example Query :
```
UNLOAD ( SELECT abc_de AS  abcDe, fgh_ij AS fghIj FROM 
        tablename  WHERE fgh_ij IN ( '123','456' ) and year = 2024 and month = 06 and day = 24
) 
TO 's3://dummy-bucketf2e78a99-gfm8/athena/data/test/' 
WITH (format='PARQUET', compression='None')
```

The results in parquet file has columns like this:
abcde , fghij

Is there any workaround or any parameter which I am missing here ?

Jen_F · Answer

Hi Rahul,

You are not missing any parameter. Athena accepts mixed case in DDL and DML queries, but lower cases the names when it executes the query. **Reference:** [Name databases, tables, and columns](https://docs.aws.amazon.com/athena/latest/ug/tables-databases-columns-names.html)

If you are not able to design your application around lower case, then the most reliable workaround is to rename columns after export using tools that support Parquet schema modification:

#### AWS Glue ETL Job
Read the Parquet files and write them back with renamed columns.

**Reference:** [AWS Glue Developer Guide](https://docs.aws.amazon.com/glue/latest/dg/what-is-glue.html)

#### Apache Spark
Use PySpark or Scala to read and rename columns.

**Reference:** [Apache Spark Documentation](https://spark.apache.org/docs/latest/)

#### Pandas (Python)
For smaller datasets:
```python
import pandas as pd
df = pd.read_parquet('s3://bucket/path/')
df.rename(columns={'abcde': 'abcDe', 'fghij': 'fghIj'}, inplace=True)
df.to_parquet('s3://bucket/new-path/')
```

**Reference:** [Pandas Documentation](https://pandas.pydata.org/docs/)

---

## Additional References

- [UNLOAD Documentation](https://docs.aws.amazon.com/athena/latest/ug/unload.html)
- [Naming Requirements for Databases, Tables, and Columns](https://docs.aws.amazon.com/athena/latest/ug/tables-databases-columns-names.html)
- [Escape reserved keywords in queries](https://docs.aws.amazon.com/athena/latest/ug/reserved-words.html)

Athena unload lowercases all camelCase columns in parquet

AWS Glue ETL Job

Apache Spark

Pandas (Python)

Additional References

Add your answer

Relevant content