I was recently bit doing a Postgres upgrade by the Postgres team considering statements like `select 1 group by true` fine to silently break in Postgres 15. See https://postgrespro.com/list/thread-id/2661353 - and this behavior remains undocumented in https://www.postgresql.org/docs/release/ . It's an absolutely incredible project, and I don't disagree with the decision to classify it as wontfix - but it's an anecdote to not rely on undefined behavior!