Michael Fuhr <mike@fuhr.org> writes:
> Maybe one of the developers can comment on why your example calls
> the function only once and mine calls it multiple times per row,
> even though they look similar.
Look at the EXPLAIN results --- one case gets flattened into a single
plan node and the other doesn't. I know exactly where that particular
skeleton is buried, too:
/* * Hack: don't try to pull up a subquery with an empty jointree. * query_planner() will correctly generate a Result
planfor a * jointree that's totally empty, but I don't think the right things * happen if an empty FromExpr appears
lowerdown in a jointree. Not * worth working hard on this, just to collapse SubqueryScan/Result * into Result... */if
(subquery->jointree->fromlist== NIL) return false;
regards, tom lane