Learning PHP, MySQL, JavaScript, and CSS, 2nd Edition

Querying a MySQL Database with PHP

The reason for using PHP as an interface to MySQL is to format the results of SQL queries in a form visible in a web page. As long as you can log in to your MySQL installation using your username and password, you can also do so from PHP. However, instead of using MySQL’s command line to enter instructions and view output, you will create query strings that are passed to MySQL. When MySQL returns its response, it will come as a data structure that PHP can recognize instead of the formatted output you see when you work on the command line. Further PHP commands can retrieve the data and format it for the web page.

The Process

The process of using MySQL with PHP is:

1. Connect to MySQL.

2. Select the database to use.

3. Build a query string.

4. Perform the query.

5. Retrieve the results and output them to a web page.

6. Repeat Steps 3 through 5 until all desired data has been retrieved.

7. Disconnect from MySQL.

We’ll work through these sections in turn, but first it’s important to set up your login details in a secure manner so people snooping around on your system have trouble getting access to your database.

Creating a Login File

Most websites developed with PHP contain multiple program files that will require access to MySQL and will therefore need your login and password details. So, it’s sensible to create a single file to store these and then include that file wherever it’s needed. Example 10-1 shows such a file, which I’ve called login.php. Type it in, replacing the username ...