Anonymous

create table nulltest (id int auto_increment primary key, name varchar(20), age int null);
insert into nulltest values(1, 'garo', 28);
insert into nulltest values(1, 'iblue', 27);
insert into nulltest values(2, 'jeguri', null);

mysql> select * from nulltest;
+----+--------+------+
| id | name   | age  |
+----+--------+------+
|  1 | garo   |   28 |
|  2 | iblue  |   27 |
|  3 | jeguri | NULL |
+----+--------+------+
3 rows in set (0.00 sec)

mysql> select avg(age), sum(age), min(age), max(age) from nulltest;
+----------+----------+----------+----------+
| avg(age) | sum(age) | min(age) | max(age) |
+----------+----------+----------+----------+
|  27.5000 |       55 |       27 |       28 |
+----------+----------+----------+----------+
1 row in set (0.00 sec)