feat: join_where?

[MarcoGorelli]

Might join_where be in-scope? I think that for Polars / DuckDB / PySpark / Ibis it should be doable, and very nice-to-have. I don't think pandas / pyarrow have equivalents, but maybe that's OK - for most of our API, it's other libraries that raise NotImplementedError, maybe it's OK if in some cases it's pandas / pyarrow that do so 😄

@camriddell this seems like it may be up your street, do you have any thoughts?

[camriddell]

@MarcoGorelli checking to see if this is still in-scope with the feature slow down.

IMO, join_where sounds like it would be great to support- can probably get the API for those that implement it pretty quickly and even add in pandas/pyarrow support via a cross join + filter?

[MarcoGorelli]

thanks for looking into this!

just noticed that this still marked as experimental and unstable in polars:

This functionality is experimental. It may be changed at any point without it being considered a breaking change.

maybe we should hold off until it stabilises in polars? which, I expect, won't be in too long