MySQL의 ASCII() 함수에 NULL을 제공하면 무엇을 반환합니까?

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

mysql> SELECT ASCII('null');
+---------------+
| ASCII('null') |
+---------------+
| 110           |
+---------------+
1 row in set (0.00 sec)

mysql> Select ASCII(NULL);
+-------------+
| ASCII(NULL) |
+-------------+
| NULL        |
+-------------+
1 row in set (0.00 sec)

mysql> Select ASCII('NULL');
+---------------+
| ASCII('NULL') |
+---------------+
| 78            |
+---------------+
1 row in set (0.00 sec)