-- Поправил
CREATE OR REPLACE FUNCTION get_all_foo() RETURNS table (a int,b text) AS
$BODY$
BEGIN
	return query
	with t as (VALUES(1,'assa' ),(2,'assa' ),(3,'assa' ))
		,t1 as (VALUES(1,'assa' ),(2,'assa' ),(3,'assa' ))
		,t2 as (VALUES(1,'assa' ),(2,'assa' ),(3,'assa' ))
		,t3 as (VALUES(1,'assa' ),(2,'assa' ),(3,'assa' ))
	select * from t3;
END
$BODY$
LANGUAGE plpgsql;

SELECT * FROM get_all_foo();

DECLARE
        .......
        t_3 TABLE [(a int ,b text)];
                        --описатель типа опционально, от возможности реализации
BEGIN
        .......
        t_3:= (SELECT ... FROM ....);
        .......
        return query SELECT * FROM t_3;
END;