Glyn Astill <glynastill(at)yahoo(dot)co(dot)uk> writes:
> I've slapped together a quick test case that gives the same results
> with explain even when I have no data in the tables and haven't
> analyzed them.
No, those aren't the same plans. In particular what's bothering me is
the lack of any sort in the first plan you showed (the one with
HashAggregate at the top). That shouldn't be possible because of the
ORDER BY --- a hash aggregate will deliver unsorted output so there
should be a sort step above it.
regards, tom lane