You could do that, but it would likely both perform significantly worse (if you're doing "analytical" kinds of queries) and be a lot less flexible and expressiv

You could do that, but it would likely both perform significantly worse (if you're doing "analytical" kinds of queries) and be a lot less flexible and expressive. But you may want to look into DuckDB, which has a sql implementation that is not ad hoc, bug ridden, slow, or incomplete (though I honestly don't know about the formality of its specification). And it is compatible with polars :)