MySQL has two different types of licensing agreements.
Open Source license (GNU) and the other more applicable to developers is their Commercial license. Below are excerpts from the MySQL documentation.
NOTE: Since Mertech’s drivers are not open source; anyone using our drivers along with MySQL must purchase a Commercial license.
GNU
The MySQL software is released under the GNU General Public License (GPL), which probably is the best-known Open Source license. The formal terms of the GPL license can be found at http://www.gnu.org/licenses/. See also http://www.gnu.org/licenses/gpl-faq.html and http://www.gnu.org/philosophy/enforcing-gpl.html. Since the MySQL software is released under the GPL, it may often be used for free, but for certain uses you may want or need to buy commercial licenses from MySQL AB at https://order.mysql.com/. Older versions of MySQL (3.22 and earlier) are subject to a stricter license. See the documentation of the specific version for information.
Please note that the use of the MySQL software under commercial license, GPL, or the old MySQL license does not automatically give you the right to use MySQL AB trademarks. See MySQL documentation section 1.4.4 MySQL AB Logos and Trademarks.
Commercial
You need a commercial license:
- When you link a program with any GPL code from the MySQL software and don’t want the resulting code to be GPL, maybe because you want to build a commercial product or keep the added non-GPL code closed source for other reasons. When purchasing commercial licenses, you are not using the MySQL software under GPL even though it’s the same code.
- When you distribute a non-GPL application that only works with the MySQL software and ship it with the MySQL software. This type of solution is actually considered to be linking even if it’s done over a network.
- When you distribute copies of the MySQL software without providing the source code as required under the GPL license.
- When you want to support the further development of the MySQL database even if you don’t formally need a commercial license…