All the data of a website is stored in databases. Database can be SQL (object oriented database) or NoSQL (graph based database, file based database, etc.). For generic applications, SQL database serves the purpose. SQL database is implemented by number of providers – MySQL, SQLite, Oracle, PostgreSQL, DB2, Microsoft SQL and others. MySQL is the most widely used SQL database engine.
There is a limit on the number of databases allowed per account. In general, one database is enough for one website. In case, you intend to host more than one website in your hosting account, you should opt for one database per website to keep the data separate and easily manageable. Before buying the hosting service, one must check if the selected plan allows the required number of databases.
If you do not like the database configuration provided by your service provider, you can buy database service from another provider. It is possible to keep one server for website and another server for database.