question about to return two diferent tables from a function

Hi, I have a question.

I have two tables

first_one

doc|date |id_custumer
1 |2005-09-22| 50
2 |2005-09-21| 50

and the second_one

doc|date |id_code
12 |2005-09-01| 20
13 |2005-09-21| 24
14 |2005-09-22| 31

then I need to join the two tables in a function like this

doc|date |id
1 |2005-09-22| 50
2 |2005-09-21| 50
12 |2005-09-01| 20
13 |2005-09-21| 24
14 |2005-09-22| 31

with just one table I don't have a problem,

CREATE OR REPLACE FUNCTION test_function()
RETURNS setof record
AS 'select * from first_one'
LANGUAGE 'sql';

CH=> select * from test_function() as result(doc int8, date date, id int8);
doc | date | id
-----+------------+----
12 | 2005-09-01 | 20
13 | 2005-09-21 | 24
14 | 2005-09-22 | 31

but I don't know how call the second table.

any help?

Thanks a lot
Luis Hildebardo Moreno
hildebardo(at)prodigy(dot)net(dot)mx
San Luis Potosi, Mexico