We have a variant of the join function that facilitates equi-join on a single join key, but we don't have one to do it for multiple join keys.
This is the existing Python API:
I think we should rename joinExprs to "on", and joinType to "how" to match Pandas. And then the "on" column should support either a string, a join condition, a list of string, or a list of join condition ("and" together).
In order to support the Python API, we'd need to add a variant for Scala as well. I think we can add another join method that looks like
and update the existing Scala one to call this one.