The MySQL Privilege Tables

Before delving into the many examples that consititute this tutorial, a brief introduction of one of the most important (and most misunderstood!) aspects of the MySQL server is in order; that is the mechanism from which MySQL secures its data and integrity: The MySQL privilege tables. The MySQL privilege tables are responsible for authenticating user access to the MySQL server, and subsequently associating those users granted access with a set of privileges. This privilege set decides what a user is capable of doing while connected to the MySQL server, controlling the user's activities on a server-wide, database, tabular and even columnar level. For example, an administrator could grant a user only enough privileges to connect to one specific MySQL database, and restrict access to all others. Furthermore, that same user might be granted only certain privileges while connected to that database, selection, insertion, and modification privileges for example. Associated with only these three privileges, that user would be denied any attempt to delete data, since the user has not been granted the deletion privilege.

For Further Reading :
http://dev.mysql.com/doc/refman/5.1/en/privilege-system.html
http://dev.mysql.com/doc/refman/5.1/en/security.html
http://dev.mysql.com/doc/refman/5.1/en/adding-users.html