apache/datafusion ? reverse-engineered prompt

Build me a fast SQL query engine in Rust that uses Apache Arrow in memory and can run analytics over files like CSV, Parquet, JSON, and Avro.

I want it to support both SQL and a DataFrame style API, with a simple command line tool so I can point it at data and run queries quickly. It should feel like a solid foundation for building custom database or data pipeline features, so make it easy to plug in new data sources, functions, and operators later.

Please include a few working examples, good error messages, and enough docs so someone can try it right away. If you need to check current crate or docs details while wiring it up, look them up online. Make sure it’s built with a clean Rust project structure and is usable as a library as well as a CLI.