Re: Returning Composite Types from C functions

Michael Fuhr <mike(at)fuhr(dot)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 plan for a
* jointree that's totally empty, but I don't think the right things
* happen if an empty FromExpr appears lower down 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