Accessing Your MySQL Database from the Web with PHP

By Luke Welling, Laura Thomson

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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

Show 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. The 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.

Listing 11.1 search.html— Book-O-Rama's Database Search Page

This HTML form is reasonably straightforward. The output of this HTML is shown in Figure 11.1.

The script that will be called when the Search button is clicked is results.php. It is listed in full in Listing 11.2. Through the course of this chapter,we discuss what this script does and how it works.

Listing 11.2 results.php—This Script Retrieves Search Results from the MySQL Database and Formats Them for Display

Note that this script allows you to enter the MySQL wildcard characters % and _ (underscore). This capability can be useful for the user,but you can escape these characters if they will cause a problem for your application.

Figure 11.2 illustrates the results of using this script to perform a search.

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