I started thinking about Tom's idea to implement functions as table
source.
To me, it seems that a very few changes are necessary:
a) parser must be changed to allow functioncall to be a table_ref
(easy)
b) when a Query node is generated out of such a call "select * from foo()"
it should be almost identical to one generated out of "select * from
(select * from foo)" with one distinction: list of query attributes should
be completed based on return type of foo().
c) executor should support execution of such Query node, properly
extracting things out of function's return value and placing them into
result attributes.
If I'm wrong, please correct me.
-alex