ABSTRACT
Modern database systems make it easy to store, retrieve, and update data on the computer. This chapter introduces database systems, the Structured Query Language (SQL) for managing databases, and writing application programs that use databases. The PHP MySQL combination makes it easy to create database-driven websites, as shown by practical examples such as shopping carts, a database for customer orders, and an interface to the PayPal payment gateway. A Database Management System usually makes databases available to many users at the same time and handles user login, privileges, and local or network access. A relational database uses multiple tables, called relations in database theory, to efficiently organize data. In fact, PHP has a built-in database system called SQLite that can be a good choice for light-duty database applications. A website can display its own login form, collect the userid and password entered by the user, and then check them against those stored in the database.
