Information from the MySQL-Website:
MySQL AB provides its software (database server, connectors, tools)
under a number of flexible licenses, designed to meet the usage and
distribution requirements of different types of users:
For Open Source Projects: If you are developing and distributing open
source applications under the GPL License, then you are free to use
MySQL under the GPL License. More Info » If you are developing and
distributing open source applications under an OSI-Approved License,
but not the GPL, MySQL provides the GPL License with a FLOSS
For Commercial OEMs, ISVs and VARs: For OEMs,
ISVs, and VARs who distribute MySQL with their products, and do not
license and distribute their source code under the GPL, MySQL provides
a flexible OEM Commercial License.
For Web Sites,
Enterprise IT, and Government IT: MySQL Enterprise is the
comprehensive subscription offering that provides database developers
and DBAs with everything they need to successfully develop and deploy
database solutions with MySQL. It includes Certified Software, updates
and upgrades, proactive alerts and advisors, the online MySQL
Knowledge Base, and full production-level technical support. The
Certified Software (database server, connectors) is provided under the
GPL License. Optionally, customers may choose a Commercial License.
At MySQL AB we believe in open source software. We encourage everyone
to publish open source software under the GPL License.
So it depends of the categorie of your project if you must/mustn't use a commecial licence.