https://duckdb.org/2024/03/29/external-aggregation.html
https://duckdb.org/2021/06/25/querying-parquet.html
If your DB is mysql or postgres, then you could read a stream from parquet, transform inline and write out to your DB
https://duckdb.org/2024/01/26/multi-database-support-in-duck...
And an unrelated, but interesting read about the parquet bomb
https://duckdb.org/2024/03/26/42-parquet-a-zip-bomb-for-the-...