again about GPL

MySQL вообще не GPL продукт - и для коммерческого применения есть масса оговорок, в том числе и приобретение лицензии. Проще с PostgresSQL- там это можно, при условии, что исходники той части проекта, которая подпадает под GPL, будут свободно доступны, можно распространять коммерческий продукт (в том числе и без исходников, если в них нет GPL кода).

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.