@dispatch(Select, ClauseElement)
def _join_selectables(a, b, condition=None, **kwargs):
    if len(a.froms) > 1:
        raise MDNotImplementedError()

    return a.replace_selectable(a.froms[0],
                                a.froms[0].join(b, condition, **kwargs))
dataset/ETHPy150Open blaze/blaze/blaze/compute/sql.py/_join_selectables/original