anything compared to NULL is always false
Actually it's null.
mysql> select false = null;
+--------------+
| false = null |
+--------------+
| NULL |
+--------------+
1 row in set (0.01 sec)
mysql> select 1 = null;
+----------+
| 1 = null |
+----------+
| NULL |
+----------+
1 row in set (0.00 sec)
mysql> select 2 = null;
+----------+
| 2 = null |
+----------+
| NULL |
+----------+
1 row in set (0.00 sec)
unknown compared to anything is unknown.
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