----------------------+
| 1 NOT IN (1, 2, NULL) |
+-----------------------+
|                     0 |
+-----------------------+

SELECT 5 NOT IN (1, 2, NULL);
+-----------------------+
| 5 NOT IN (1, 2, NULL) |
+-----------------------+
|                  NULL |
+-----------------------+

URL: https://mariadb.com/kb/en/not-in/https://mariadb.com/kb/en/not-in/