PostgreSQL: Call a Function More Than Once in FROM Clause - function

Question

How can I call a function which returns records more than once in FROM clause? I understand that I have to specify a 'column definition list' when using a function that returns records. But how can I then use aliases for that function?
Example:
CREATE OR REPLACE FUNCTION foo(which_foo int) RETURNS SETOF RECORD AS
$BODY$BEGIN
IF which_foo=0 THEN
RETURN QUERY EXECUTE 'SELECT 1::int,2::int;';
ELSE
RETURN QUERY EXECUTE 'SELECT 1::int,2::int;';
END IF;
END$BODY$
LANGUAGE plpgsql;
SELECT * FROM foo(0) AS (a int, b int);;
SELECT * FROM foo(1) AS (c int, d int);
SELECT * FROM foo(0) AS (a int, b int), foo(1) AS (c int, d int);
The last select statement will fail with:
ERROR: table name "foo" specified more than once
I want to keep using the column definition list, because the function I want to use in the end has to be as generic as possible.

Answer 1

SELECT f0.*, f1.*
FROM
foo(0) AS f0 (a int, b int),
foo(1) AS f1 (c int, d int);

Answer 2

I understand that I have to specify a 'column definition list' when
using a function that returns records.
No, you do not. I wouldn't operate with anonymous records. Declare the return type, since you already know it:
CREATE OR REPLACE FUNCTION foo(which_foo int)
RETURNS TABLE (a int, b int) AS
$func$
BEGIN
IF which_foo = 0 THEN
RETURN QUERY SELECT 1,2;
ELSE
RETURN QUERY SELECT 1,2;
END IF;
END
$func$ LANGUAGE plpgsql;
And assuming you do not want to combine multiple calls into one row, you should use UNION ALL:
SELECT * FROM foo(0)
UNION ALL
SELECT * FROM foo(1);