The AUTO_INCREMENT attribute can be used to generate a unique identity for new rows:
mysql>
mysql> CREATE TABLE employee (
-> id MEDIUMINT NOT NULL AUTO_INCREMENT,
-> name CHAR(30) NOT NULL,
-> PRIMARY KEY (id)
-> );
Query OK, 0 rows affected (0.01 sec)
mysql>
mysql> desc employee;
+-------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+----------------+
| id | mediumint(9) | NO | PRI | NULL | auto_increment |
| name | char(30) | NO | | | |
+-------+--------------+------+-----+---------+----------------+
2 rows in set (0.02 sec)
mysql>
mysql> INSERT INTO employee (name) VALUES ('A'),
-> ('B'),
-> ('C'),
-> ('D'),
-> ('E'),
-> ('F');
Query OK, 6 rows affected (0.00 sec)
Records: 6 Duplicates: 0 Warnings: 0
mysql>
mysql> SELECT * FROM employee;
+----+------+
| id | name |
+----+------+
| 1 | A |
| 2 | B |
| 3 | C |
| 4 | D |
| 5 | E |
| 6 | F |
+----+------+
6 rows in set (0.00 sec)
mysql>
mysql> drop table employee;
Query OK, 0 rows affected (0.00 sec)
mysql>