MySQL software is Open Source:

from the Internet and use it without paying anything. If you wish, you may study the source code and change it to suit your needs. The MySQL software uses the GPL (GNU General Public License), http://www.fsf.org/licenses/, to define what you may and may not do with the software in different situations. If you feel uncomfortable with the GPL or need to embed MySQL code into a commercial application, you can buy a commercially licensed version from us. See the MySQL Licensing Overview for more information (http://www.mysql.com/company/legal/licensing/).

ORACLE

Oracle is one of the largest vendors in the enterprise IT market and the shorthand name of its flagship product, a relational database management system (RDBMS) that's formally called Oracle Database. The database software sits at the center of many corporate IT environments, supporting a mix of transaction processing, business intelligence and analytics applications.

Oracle Database's architecture

Like other RDBMS software, Oracle Database is built on top of SQL, a standardized programming language that database administrators, data analysts and other IT professionals use to manage databases and query the data stored in them. The Oracle software is tied to PL/SQL, an implementation developed by Oracle that adds a set of proprietary programming extensions to standard SQL -- a common practice among RDBMS vendors. Oracle Database also supports programming in Java, and programs written in PL/SQL or Java can be called from the other language.