Mysql, функция COUNT

[sql]
(topas@localhost) [test]>describe test
-> ;
+-------+---------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| idt | int(11) | YES | | NULL | |
| n | int(11) | YES | | NULL | |
| n2 | int(11) | YES | | NULL | |
+-------+---------+------+-----+---------+----------------+
4 rows in set (0.05 sec)

(topas@localhost) [test]>insert into `test` values
-> (1, 2, 10, 0),
-> (2, 2, 10, 0),
-> (3, 2, 10, 0),
-> (4, 2, 10, 5),
-> (5, 2, 20, 0),
-> (6, 2, 20, 0),
-> (7, 3, 20, 0);
Query OK, 7 rows affected (0.00 sec)
Records: 7 Duplicates: 0 Warnings: 0

(topas@localhost) [test]>select * from `test`
-> ;
+----+------+------+------+
| id | idt | n | n2 |
+----+------+------+------+
| 1 | 2 | 10 | 0 |
| 2 | 2 | 10 | 0 |
| 3 | 2 | 10 | 0 |
| 4 | 2 | 10 | 5 |
| 5 | 2 | 20 | 0 |
| 6 | 2 | 20 | 0 |
| 7 | 3 | 20 | 0 |
+----+------+------+------+
7 rows in set (0.00 sec)

(topas@localhost) [test]>select count(id) from test where idt = 2 and n=10 and n2 <= 0;
+-----------+
| count(id) |
+-----------+
| 3 |
+-----------+
1 row in set (0.09 sec)

(topas@localhost) [test]>
[/sql]