MySQL Is Open Source, But Not Necessarily Free (ISVs, read)
A brief discussion among the more tech-savvy friends started a small debate - whether or not MySQL is free for independent software vendors (ISVs). Personally, I've heard that it is not, but because I've mostly used Oracle in my projects, it wasn't a concern for me. However, the debate sparked interest because MySQL is downloadable and can be used without much thought, most ISVs use it without knowing that unless their application is going to be GPL-ed, they actually need a license (there are some workarounds involving using a fork of MySQL or using a non-standard JDBC driver).
Read the snippets below for brief licensing information.
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Special MySQL Considerations
MySQL software is a well-know case of software with a dual-license. The basic orientation is provided here:
http://www.mysql.com/products/which-edition.html
http://www.mysql.com/about/legal/licensing/oem/
If you want to use MySQL as a commercial distributor (OEM, ISV or VAR) use a commercial license, you must purchase a commercial license.
Otherwise, you can use MySQL Community Edition and Community Server under GNU GPL v2.0. Your software must be compatible with this license, and you may, but do not have to, distribute MySQL with your software.
If your software is FOSS (GPL v2.0 or license listed here, including BSD and LGPL, you can distribute MySQL drivers, namely Community Edition or Community Server Client Libraries, but not MySQL database.
Although the use of a database can be treated as aggregate use, your application is effectively bound to MySQL by usage of MySQL Client Libraries (MySQL Drivers", "MySQL Connectors", including i Java, .NET, ODBC, PHP i C++ connectors and drivers) and related licensing requirements (commercial, GPL v2, or those of MySQL FLOSS exception.
The usage of MySQL drivers through mediation of an application server also seems to be treated as linking and not as aggregation, even if effectively performed the means of XML configuration, annotations (or methods like lookup, Java reflection, or inheritance). These limitations cannot be averted by independent distribution of MySQL database under GPL, usage of MySQL Enterprise drivers, or by silent letting of end-user to install the MySQL database and drivers.
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Source: http://www.mysql.com/about/legal/licensing/oem/#1
Q3: As a commercial OEM, ISV or VAR, when should I purchase a commercial license for MySQL software?
A: OEMs, ISVs and VARs that want the benefits of embedding commercial binaries of MySQL software in their commercial applications but do not want to be subject to the GPL and do not want to release the source code for their proprietary applications should purchase a commercial license from Sun. Purchasing a commercial license means that the GPL does not apply, and a commercial license includes the assurances that distributors typically find in commercial distribution agreements.