A web database is a system for storing information that can then be accessed via a website. For example, an online community may have a database that stores the username, password, and other details of all its members. The most commonly used database system for the internet is MySQL due to its integration with PHP — one of the most widely used server side programming languages. At its most simple level, a web database is a set of one or more tables that contain data. Each table has different fields for storing information of various types. These tables can then be linked together in order to manipulate data in useful or interesting ways. In many cases, a table will use aprimary key, which must be unique for each entry and allows for unambiguous selection of data. A web database can be used for a range of different purposes. Each field in a table has to have a defined data type. For example, numbers, strings, and dates can all be inserted into a web database. Proper database design involves choosing the correct data type for each field in order to reduce memory consumption and increase the speed of access. Although for small databases this often isn't so important, big web databases can grow to millions of entries and need to be well designed to work effectively.