MySQL is the database system commonly used to store data used by website servers. It is a free to use system and is easily interfaced with the common Apache web server system. It is therefore much more common for use in general purpose website design and development, but still has the power and complexity if necessary that larger database system such as SQL Server and Oracle can provide.
I have been programming in SQL for many years and have experience working with database systems much more complex than the average website required by a small company, so even if your requirements are a little more complex than the average I can easily design and implement the required database structure for you to provide the backbone for your website.