"Steven D.Arnold" <stevena(at)neosynapse(dot)net> writes:
> Query (2) below is the same query, but we reverse the order of the
> tables. It's obviously not quite the same query semantically, even
> though in my case it should always produce the same result.
Since it is in fact not the same query, I'm unclear on why you expect
it to produce the same plan.
> I'm using version 7.3.4 of Postgres.
FWIW, I believe that 7.4 will recognize that (1) and (3) are
semantically equivalent.
regards, tom lane