SQL PRIMARY KEY
SQL PRIMARY KEY uniquely identifies each record in a database table.
Primary keys must contain unique values and primary key column cannot contain NULL
values. A table can not have more than one primary key .
Example
mysql> CREATE TABLE `new_users` (`id` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(255) NOT NULL, PRIMARY KEY (`id`));
Query OK, 0 rows affected (0.10 sec)
Beginner's Guide....
