grouped joins should almost always be left joins

[default-kramer]

It seems like we could have better default behavior here. Perhaps by default, all grouped joins should be left joins. Then (join-type #f) would mean "left join for grouped joins, infer for all other joins." And (join-type 'infer) would mean "infer, even if this is a grouped join."

Or perhaps define-schema, specifically #:has-group, is a better place for this opinion.