relational database design

mysql> CREATE TABLE games (
    -> game_id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
    -> game_name VARCHAR(150) NOT NULL);
Query OK, 0 rows affected (0.03 sec)

mysql> CREATE TABLE genres (
    -> genre_id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
    -> genre_name VARCHAR(100) NOT NULL);
Query OK, 0 rows affected (0.00 sec)

mysql> CREATE TABLE relation (
    -> game_id INT NOT NULL,
    -> genre_id INT NOT NULL,
    -> UNIQUE KEY(game_id, genre_id));
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO games (game_name) VALUES ('Unreal Tournament'),('FIFA 2002'),('Grand Theft Auto III');
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> INSERT INTO genres (genre_name) VALUES ('Action'),('Adventure'),('Role-playing'),('Simulation'),('Strategy'),('Sports');
Query OK, 6 rows affected (0.00 sec)
Records: 6  Duplicates: 0  Warnings: 0

mysql> INSERT INTO relation VALUES (1,1),(3,1),(2,6),(3,2);
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> SELECT * FROM relation;
+---------+----------+
| game_id | genre_id |
+---------+----------+
|       1 |        1 |
|       2 |        6 |
|       3 |        1 |
|       3 |        2 |
+---------+----------+
4 rows in set (0.00 sec)

mysql> SELECT a.game_name, b.genre_name FROM games a INNER JOIN relation r USING (game_id) INNER JOIN genres b USING (genre_id);
+----------------------+------------+
| game_name            | genre_name |
+----------------------+------------+
| Unreal Tournament    | Action     |
| Grand Theft Auto III | Action     |
| FIFA 2002            | Sports     |
| Grand Theft Auto III | Adventure  |
+----------------------+------------+
4 rows in set (0.00 sec)

mysql> SELECT b.genre_name, COUNT(a.game_id) AS howmany FROM genres b LEFT JOIN relation r USING (genre_id) LEFT JOIN games a USING (game_id) GROUP BY b.genre_name;
+--------------+---------+
| genre_name   | howmany |
+--------------+---------+
| Action       |       2 |
| Adventure    |       1 |
| Role-playing |       0 |
| Simulation   |       0 |
| Sports       |       1 |
| Strategy     |       0 |
+--------------+---------+
6 rows in set (0.00 sec)