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.