CREATE TABLE t1 (id int);
CREATE TABLE t2 (id int);
INSERT INTO t1 VALUES (1), (2), (2);
INSERT INTO t2 VALUES (2), (3);

SELECT t1.id, t2.id FROM t1 LEFT JOIN t2 USING (id)
UNION ALL
SELECT t1.id, t2.id FROM t1 RIGHT JOIN t2 USING (id);

/*
+------+------+
| id   | id   |
+------+------+
|    1 | NULL |
|    2 |    2 |
|    2 |    2 |
|    2 |    2 |
|    2 |    2 |
| NULL |    3 |
+------+------+
6 rows in set (0.00 sec)

Too many.
*/


SELECT t1.id, t2.id FROM t1 LEFT JOIN t2 USING (id)
UNION
SELECT t1.id, t2.id FROM t1 RIGHT JOIN t2 USING (id);

/*
+------+------+
| id   | id   |
+------+------+
|    1 | NULL |
|    2 |    2 |
| NULL |    3 |
+------+------+
3 rows in set (0.00 sec)

Too few.
*/

select * from t1 left outer join t2 on (t1.id=t2.id)  
union all 
select * from t1 right outer join t2 on (t1.id=t2.id) where t1.id is null;

/*
+------+------+
| id   | id   |
+------+------+
|    1 | NULL |
|    2 |    2 |
|    2 |    2 |
| NULL |    3 |
+------+------+
4 rows in set (0.00 sec)


*/