Most of the database design we do is executed in MySQL.
It is robust, scaleable, secure, fast, easy to implement, easy to connect to and supported by pretty much every hosting company. All our hosting packages support MySQL. One could say that a hosting company that does not provide support for MySQL databases is not really a hosting company at all. Once could even say that a developer that does not know how to use MySQL is not really a developer. Maybe that is a little unfair...
It is the backbone of more web sites than any other database and there are more open source applications, content managment systems, e-commerce solutions that are based on MySQL than any other database technology.
It is not the only database we design in (see MongoDB, MS SQL, CouchDB, AWS, etc) but it is the one we use when we do not have to do something quite unusual. It scales up well beyond most needs and has a feature set that meets most requirements. And it is free, as in free.
MySQL is not married to PHP but they have a pretty good relationship and very seldom fall out with each other - they grew up next door and understand each other intuitively.
If you have a database project in mind, need a MySql database designed or simply need to consult a database specialist, please give us a call.