Postgres has the having clause. If it didn’t, that wouldn’t work, as you can’t use aggregates in a where. If you have to make do without having, for some reason, you can use a subquery, something like select * from (select someCalculatedValue(someInput) as lol) as stuff where lol > 42, which is very verbose, but doesn’t cause the sync problem.
Also, I don’t think they were saying the capability having gives is bad, but that a new query language should be designed such that you get that capability without it.