create function get_rel(
    out _id integer,
    out _name varchar
) returns setof record as $$
begin
    return query select 11, cast('foobar' as varchar);
end
$$ language plpgsql;

select * from get_rel();

create function get_rel(
    out _id integer
) returns setof record as $$
begin
    return query select 11;
end
$$ language plpgsql;

select * from get_rel();