Accessing Your MySQL Database from the Web with PHP

Learn how to access a MySQL database from the Web using PHP, including how to read from and write to the database and how to filter potentially troublesome input data.

This chapter is an excerpt from the new 4th Ed. of "PHP and MySQL Web Development" authored by Luke Welling and Laura Thomson, published by SAMS, ISBN 0672329166, Copyright 2009 by Pearson Education, Inc. For more info, please visit www.informit.com. Safari Books Online subscribers can read it here: http://safari.informit.com/9780672329166.

Previously, in our work with PHP, we used a flat file to store and retrieve data. When we looked at this file in Chapter 2, “Storing and Retrieving Data,” we mentioned that relational database systems make a lot of these storage and retrieval tasks easier, safer, and more efficient in a web application. Now, having worked with MySQL to create a database, we can begin connecting this database to a web-based front end.

In this chapter, we explain how to access the Book-O-Rama database from the Web using PHP. You learn how to read from and write to the database and how to filter potentially troublesome input data.

Key topics covered in this chapter include

• How web database architectures work
• Querying a database from the Web using the basic steps
• Setting up a connection
• Getting information about available databases
• Choosing a database to use
• Querying the database
• Retrieving the query results
• Disconnecting from the database
• Putting new information in the database
• Using prepared statements
• Using other PHP-database interfaces
• Using a generic database interface: PEAR MDB2

How Web Database Architectures Work

In Chapter 8, “Designing Your Web Database,” we outlined how web database architectures work. Just to remind you, here are the steps:

1. A user’s web browser issues an HTTP request for a particular web page. For example, the user might have requested a search for all the books written by Michael Morgan at Book-O-Rama, using an HTML form. The search results page is called results.php
2. The web server receives the request for results.php, retrieves the file, and passes it to the PHP engine for processing.
3. PHP engine begins parsing the script. Inside the script is a command to connect to the database and execute a query (perform the search for books). PHP opens a connection to the MySQL server and sends on the appropriate query.
4. The MySQL server receives the database query, processes it, and sends the results—a list of books—back to the PHP engine.
5. The PHP engine finishes running the script. This usually involves formatting the query results nicely in HTML. It then returns the resulting HTML to the web server.
6. The web server passes the HTML back to the browser, where the user can see the list of books she requested.

Now you have an existing MySQL database, so you can write the PHP code to perform the preceding steps. Begin with the search form. The code for this plain HTML form is shown in Listing 11.1.

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