Используй вьюху для вывода....

CREATE TABLE t2 (d2 DATE, val2 NUMBER)
/
INSERT INTO t1
VALUES (SYSDATE, 20)
/
INSERT INTO t1
VALUES (SYSDATE + 1, 50)
/
INSERT INTO t1
VALUES (SYSDATE + 2, 5)
/
INSERT INTO t2
VALUES (SYSDATE, 24)
/
INSERT INTO t2
VALUES (SYSDATE - 1, 80)
/
INSERT INTO t2
VALUES (SYSDATE - 2, 100)
/
CREATE VIEW vw_t
AS
(SELECT a.d1, a.val1, NULL AS val2
FROM t1 a
UNION ALL
SELECT a.d2, NULL AS val1, a.val2
FROM t2 a)
/

а вобще Fast Report лучше....