This is also really kind of an artifact of how GROUP BY works in most database engines. I've always liked the way MySQL/MariaDB let you omit things from the GR

This is also really kind of an artifact of how GROUP BY works in most database engines. I've always liked the way MySQL/MariaDB let you omit things from the GROUP BY if they're provably unique in each group (here, if foo_id is a primary key of foo, and you're grouping by it, there can only ever be one foo.some_float for each foo_id). I suspect in practice this would get rid of approximately all occurrences of group-by-float.