Learning PHP, MySQL, and JavaScript

The Benefits of PHP, MySQL, and JavaScript

At the start of this chapter, I introduced the world of Web 1.0, but it wasn’t long before the rush was on to create Web 1.1, with the development of such browser enhancements as Java, JavaScript, JScript (Microsoft’s slight variant of JavaScript) and ActiveX. On the server side, progress was being made on the Common Gateway Interface (CGI) using scripting languages such as Perl (an alternative to the PHP language) and server-side scripting—inserting the contents of one file (or the output of a system call) into another one dynamically.

Once the dust had settled, three main technologies stood head and shoulders above the others. Although Perl was still a popular scripting language with a strong following, PHP’s simplicity and built-in links to the MySQL database program had earned it more than double the number of users. And JavaScript, which had become an essential part of the equation for dynamically manipulating CSS (Cascading Style Sheets) now took on the even more muscular task of handling the client side of the Ajax process. Under Ajax, web pages perform data handling and send requests to web servers in the background—without the web user being aware that this is going on.

No doubt the symbiotic nature of PHP and MySQL helped propel them both forward, but what attracted developers to them in the first place? The simple answer has to be the ease with which you can use them to quickly create dynamic elements on websites. MySQL is a fast and powerful yet easy-to-use database system that offers just about anything a website would need in order to find and serve up data to browsers. When PHP allies with MySQL to store and retrieve this data, you have the fundamental parts required for the development of social networking sites and the beginnings of Web 2.0.

Using PHP

With PHP, it’s a simple matter to embed dynamic activity in web pages. When you give pages the .php extension, they have instant access to the scripting language. From a developer’s point of view, all you have to do is write code such as the following:

<?php
echo "Hello World. Today is ".date("l").". ";
?>

How are you?

The opening <?php tells the web server to allow the PHP program to interpret all the following code up to the ?> command. Outside of this construct, everything is sent to the client as direct HTML. So the text “How are you?” is simply output to the browser; within the PHP tags, the built-in date function displays the current day of the week according to the server’s system time.

The final output of the two parts looks like this:

Hello World. Today is Wednesday. How are you?

PHP is a flexible language, and some people prefer to place the PHP construct directly next to PHP code, like this:

Hello World. Today is <?php echo date("l"); ?>. How are you?

There are also other ways of formatting and outputting information, which I’ll explain in the chapters on PHP. The point is that with PHP, web developers have a scripting language that although not as fast as compiling your code in C or a similar language, is incredibly speedy and that also integrates seamlessly with HTML code.

Note

If you intend to type in the PHP examples in this book to work along with me, you must remember to add <?php in front and ?> after them to ensure that the PHP interpreter processes them. To facilitate this, you may wish to prepare a file called example.php with those tags in place.

Using PHP, you have unlimited control over your web server. Whether you need to modify HTML on the fly, process a credit card, add user details to a database, or fetch information from a third-party website, you can do it all from within the same PHP files in which the HTML itself resides.

Using MySQL

Of course, there’s not a lot of point to being able to change HTML output dynamically unless you also have a means to track the changes that users make as they use your website. In the early days of the Web, many sites used “flat” text files to store data such as usernames and passwords. But this approach could cause problems if the file wasn’t correctly locked against corruption from multiple simultaneous accesses. Also, a flat file can get only so big before it becomes unwieldy to manage—not to mention the difficulty of trying to merge files and perform complex searches in any kind of reasonable time.

That’s where relational databases with structured querying become essential. And MySQL, being free to use and installed on vast numbers of Internet web servers, rises superbly to the occasion. It is a robust and exceptionally fast database management system that uses English-like commands.

The highest level of MySQL structure is a database, within which you can have one or more tables that contain your data. For example, let’s suppose you are working on a table called users, within which you have created columns for surname, firstname, and email, and you now wish to add another user. One command that you might use to do this is:

INSERT INTO users VALUES('Smith', 'John', '[e-mail]');

Of course, as mentioned earlier, you will have issued other commands to create the database and table and to set up all the correct fields, but the INSERT command here shows how simple it can be to add new data to a database. The INSERT command is an example of SQL (which stands for “Structured Query Language”), a language designed in the early 1970s and reminiscent of one of the oldest programming languages, COBOL. It is well suited, however, to database queries, which is why it is still in use after all this time.

It’s equally easy to look up data. Let’s assume that you have an email address for a user and need to look up that person’s name. To do this, you could issue a MySQL query such as:

SELECT surname,firstname FROM users WHERE email='[e-mail]';

MySQL will then return Smith, John and any other pairs of names that may be associated with that email address in the database.

As you’d expect, there’s quite a bit more that you can do with MySQL than just simple INSERT and SELECT commands. For example, you can join multiple tables according to various criteria, ask for results in a variety of different orders, make partial matches when you know only part of the string that you are searching for, return only the nth result, and a lot more.

Using PHP, you can make all these calls directly to MySQL without having to run the MySQL program yourself or use its command-line interface. This means you can save the results in arrays for processing and perform multiple lookups, each dependent on the results returned from earlier ones, to drill right down to the item of data you need.

For even more power, as you’ll see later, there are additional functions built right in to MySQL that you can call up for common operations and extra speed.

Using JavaScript

The oldest of the three core technologies in this book, JavaScript, was created to enable scripting access to all the elements of an HTML document. In other words, it provides a means for dynamic user interaction such as checking email address validity in input forms, displaying prompts such as “Did you really mean that?”, and so on (although it cannot be relied upon for security) which should always be performed on the web server.

Combined with CSS, JavaScript is the power behind dynamic web pages that change in front of your eyes rather than when a new page is returned by the server.

However, JavaScript can also be tricky to use, due to some major differences among the ways different browser designers have chosen to implement it. This mainly came about when some manufacturers tried to put additional functionality into their browsers at the expense of compatibility with their rivals.

Thankfully, the manufacturers have mostly now come to their senses and have realized the need for full compatibility between each other, so web developers don’t have to write multiexception code. But there remain millions of legacy browsers that will be in use for a good many years to come. Luckily, there are solutions for the incompatibility problems, and later in this book we’ll look at libraries and techniques that enable you to safely ignore these differences.

For now, let’s take a quick look at how you can use basic JavaScript, accepted by all browsers:

<script type="text/javascript">
document.write("Hello World. Today is " + Date() );
</script>

This code snippet tells the web browser to interpret everything within the script tags as JavaScript, which the browser then does by writing the text “Hello World. Today is ” to the current document, along with the date, by using the JavaScript function Date. The result will look something like this:

Hello World. Today is Sun Jan 01 2012 14:14:00

Note

It’s worth knowing that unless you need to specify an exact version of JavaScript, you can normally omit the type="text/javascript" and just use <script> to start the interpretation of the JavaScript.

As previously mentioned, JavaScript was originally developed to offer dynamic control over the various elements within an HTML document, and that is still its main use. But more and more, JavaScript is being used for Ajax. This is a term for the process of accessing the web server in the background. (It originally meant “Asynchronous JavaScript and XML,” but that phrase is already a bit outdated.)

Ajax is the main process behind what is now known as Web 2.0 (a term coined by Tim O’Reilly, the founder and CEO of this book’s publishing company), in which web pages have started to resemble standalone programs, because they don’t have to be reloaded in their entirety. Instead, a quick Ajax call can pull in and update a single element on a web page, such as changing your photograph on a social networking site or replacing a button that you click with the answer to a question. This subject is fully covered in Chapter 18.