Stuff

mysql> select * from fun;
+------+
| i    |
+------+
| 1    |
| 3    |
| NULL |
+------+
3 rows in set (0.00 sec)


mysql> select avg(i) from fun;
+-----------------+
| avg(i)          |
+-----------------+
| 1.3333333333333 |
+-----------------+