Microsoft has its own version of SQL, called MS SQL. Like MySQL and PostgreSQL it is a very powerful database solution, but only available on Windows servers. It is widely used for commercial applications, but Windows/MS SQL hosting is more expensive than Linux/MySql hosting, and there are fewer online resources for MS SQL.
Microsoft Access
Another database from Microsoft that you may well have heard of is Access, and it is available in many cheap Windows hosting packages. It is not to as efficient and scalable as SQL databases, but price is its strength if you need Windows hosting and have a low traffic application.
