Re: Condition pushdown: why (=) is pushed down into join, but BETWEEN or >= is not?

I don't think 0001 is right either, although maybe for somewhat
different reasons. First, I think it only considers VAR OP CONST style
clauses, but that is leaving money on the table, because given a.x =
b.x AND mumble(a.x), we can decide to instead test mumble(b.x) if the
equality operator in question has is-binary-identical semantics. It
does not seem necessary for a first patch to deal with both that and
the somewhat more pleasing case where we're making deductions based on
operator families ... but we shouldn't commit to a design for the VAR
OP CONST case without understanding how it could be generalized.

Second, it looks to me like the patch takes the rather naive strategy
of enforcing the derived clauses everywhere that they can legally be
put, which seems certain not to be optimal.