When I send the mail, I saw it, the problem is that the function
should return setof void instead of void, then it works, sorry for
bothering.
pv=# --increase every a in foo by 1, but now in function
create or replace function foofunc2() returns setof void as
$func$
select foofunc(a) from foo
$func$ language sql;
pv=# select foofunc2();
foofunc2
----------
(3 rows)
pv=# select * from foo;
a
-----
1
11
101
(3 rows)