MySQL is distributed under GPL v2, but there are some licensing exceptions
that allow the client libraries to be linked with a non-GPL application,
so long as the application is under a license approved by Oracle.
For details see
 
http://www.mysql.com/about/legal/licensing/foss-exception/
 
Some innobase code from Percona and Google is under BSD license.
Some code related to test-suite is under LGPLv2.