returns 0 row from plpgsql function

2010/3/20 zhong ming wu <mr.z.m.wu@gmail.com>:

Dear List

I use plpgsql function as a postfix mailserver look-up table.  For
example to look up virtual email address.
If I don't host this email address, then the function returns null.
Because it's a 1 row of null value postfix logs a warning message.
Although it's harmless in that postfix takes no further action to
deliver mail, these warning messages fill up log table.

How can I return 0 row from plpgsql function?

create or replace function func(...)
returns setof tablename as $$
begin
return;
end;
$$ language plpgsql;

select * from func(..);

regards
Pavel Stehule