MySQL Licensing Policy
The formal terms of the GPL license can be found at section J  GNU GENERAL PUBLIC LICENSE. For pricing and ordering information, see https:// order.mysql.com/.
Basically, our licensing policy and interpretation of the GPL is as follows:
For normal internal use, MySQL costs nothing.  You do not have to pay us if you do not want to.
A license is required if:
You link a program, that is not free software, with code from the MySQL server or clients that has the GPL copyright. This happens for example when you use MySQL as an embedded server in your applications or when you add not free extensions to the MySQL server.  In this case your application/code would also become GPL through the GPL license that acts as a virus.  By licensing MySQL server from MySQL AB under a commercial license you will avoid this problem. See http://www.gnu.org/copyleft/gpl-faq.html.
You have a commercial application that ONLY works with MySQL and ships the application with the MySQL server.  This is because we view this as linking even if it is done over the network. 
You have a distribution of MySQL and you don't provide the source code for your copy of the MySQL server, as defined in the GPL license.
A license is not required if:
You include the MySQL client code in a commercial program.  The client part of MySQL is licensed under the LGPL GNU Library General Public License.  The mysql command-line client does include code from the readline library that is under the GPL, however.
If your use of MySQL does not require a license, but you like MySQL and want to encourage further development, you are certainly welcome to purchase a license or MySQL support anyway. See section 1.5.1  Support offered by MySQL AB.
If you use MySQL in a commercial context such that you profit by  its use, we ask that you further the development of MySQL by  purchasing some level of support. We feel that if MySQL helps  your business, it is reasonable to ask that you help MySQL.   (Otherwise, if you ask us support questions, you are not only using for free something into which we've put a lot a work, you're asking us to  provide free support, too.)
Note that older versions of MySQL are still using a more strict license. See the documentation for the specific version for more information.
For circumstances under which a MySQL license is required, you need a license per machine that runs the mysqld server.  However, a multiple-CPU machine counts as a single machine, and there is no restriction on the number of MySQL servers that run on one machine, or on the number of clients concurrently connected to a server running on that machine.
If you have any questions as to whether or not a license is required for your particular use of MySQL, please read this again and then contact us.  See section 1.1.2.1  Contact Information.
If you require a MySQL license, the easiest way to pay for it is to use the license form on MySQL's secure server at https://order.mysql.com/. You can also get the latest pricing and ordering information by sending an e-mail to sales@mysql.com.