mysql>
mysql> SELECT 1 IS NOT UNKNOWN, 0 IS NOT UNKNOWN, NULL IS NOT UNKNOWN;
+------------------+------------------+---------------------+
| 1 IS NOT UNKNOWN | 0 IS NOT UNKNOWN | NULL IS NOT UNKNOWN |
+------------------+------------------+---------------------+
| 1 | 1 | 0 |
+------------------+------------------+---------------------+
1 row in set (0.00 sec)
mysql>