mysql>
mysql> SELECT 1 XOR NULL;
+------------+
| 1 XOR NULL |
+------------+
| NULL |
+------------+
1 row in set (0.00 sec)
mysql> SELECT NULL XOR NULL;
+---------------+
| NULL XOR NULL |
+---------------+
| NULL |
+---------------+
1 row in set (0.00 sec)
mysql>