你可以用一个FULL OUTER JOIN（而不是你的查询，SELECT从表中s 4次，使用2个MINUS es和一个UNION ALL）：

SELECT CASE
       WHEN a.num IS NOT NULL
       THEN 'only A'
       ELSE 'only B'
       END AS what,
       COALESCE(a.num, b.num) AS num,
       CASE
       WHEN a.num IS NOT NULL
       THEN a.txt
       ELSE b.txt
       END AS txt
FROM   aaa a
       FULL OUTER JOIN bbb b 
       ON a.num = b.num AND a.txt = b.txt
WHERE  a.num IS NULL
OR     b.num IS NULL
ORDER BY num, what

其中，对于样本数据：

CREATE TABLE AAA(NUM,TXT) AS
SELECT 1,   'One'   FROM DUAL UNION ALL
SELECT 2,   'too'   FROM DUAL UNION ALL
SELECT 3,   'Three' FROM DUAL UNION ALL
SELECT 4,   'Four'  FROM DUAL;

CREATE TABLE BBB(NUM,TXT) AS
SELECT 1,   'One'  FROM DUAL UNION ALL
SELECT 3,   NULL   FROM DUAL UNION ALL
SELECT 4,   'Four' FROM DUAL UNION ALL
SELECT 2,   'Two'  FROM DUAL UNION ALL
SELECT 5,   'Five' FROM DUAL;

输出：
| 什么|NUM| TXT|
| - -----|- -----|- -----|
| 只有A| 2|太|
| 只有B| 2|两个|
| 只有A| 3|三个|
| 只有B| 3|联系我们|
| 只有B| 5个|五|
fiddle

样本数据：

SQL> with
  2  aaa (num, txt) as
  3    (select 1, 'One'   from dual union all
  4     select 2, 'too'   from dual union all
  5     select 3, 'Three' from dual union all
  6     select 4, 'Four'  from dual
  7    ),
  8  bbb (num, txt) as
  9    (select 1, 'One'  from dual union all
 10     select 2, 'Two'  from dual union all
 11     select 3, null   from dual union all
 12     select 4, 'Four' from dual union all
 13     select 5, 'Five' from dual
 14    )

查询：

15  select 'only A' what, a.* from aaa a minus select 'only A', b.* from bbb b
 16  union all
 17  select 'only B' what, b.* from bbb b minus select 'only B', a.* from aaa a
 18  order by 2, 1;

WHAT          NUM TXT
------ ---------- -----
only A          2 too
only B          2 Two
only A          3 Three
only B          3
only B          5 Five

SQL>