You can name the groups, there’s no schema for your group by response.

I can have a join on a cte or tmp table, then I’m out of the usual checks.

You can also have old code running on new schema, so better that it dies on load.

> join on a cte

I’ll grant you that this can generate NULLs in a variety of ways (implicit type conversion, for one), but I also think that those issues could be caught via linting if nothing else. I’ll also grant you that this is shifting the goalposts a bit.

> old code running on new schema

Yeah, this would be the primary offender. I was thinking of perfect schema:code coupling, without needing to worry about other people doing dastardly things, but that’s sadly unrealistic for many orgs.