Microsoft SQL Server is a Relational Database Management System (RDBMS) that supports a wide variety of transaction processing, business intelligence and analytics applications in corporate IT environments.

Oracle is used by many large organizations, start-ups and beginners alike.

MySQL is free and open-source software under the terms of the GNU General Public License, and is also available under a variety of proprietary licenses. MySQL was owned and sponsored by the Swedish company MySQL AB, which was bought by Sun Microsystems (now Oracle Corporation).

PostgreSQL is a powerful, open source object-relational database system that uses and extends the SQL language combined with many features that safely store and scale the most complicated data workloads.