> In theory, you could parse the SQL and build up some kind of AST on which compatibility could be built.

This is an interesting problem that I'd like to learn more about. Have you read anything about it?

You can compose SQL with https://ibis-project.org/tutorials/ibis-for-sql-users, which is using https://github.com/tobymao/sqlglot to parse the SQL under the hood.

As an alternative to parsing the SQL yourself, DuckDB's https://duckdb.org/docs/api/python/relational_api allows you to compose SQL expressions efficiently and lazily, which I've used when playing around with things like https://gist.github.com/ajfriend/eea0795546c7c44f1c24ab0560a...