Publishers of technology books, eBooks, and videos for creative people

Home > Articles > Web Design & Development > PHP/MySQL/Scripting

From the book What Is PHP? What Does It Do?

What Is PHP? What Does It Do?

PHP is a server-side technology that builds web pages dynamically. Let’s say you have a product catalog. Instead of updating your web pages each time a product is added or removed, you can store the details in a database and use PHP to query the database and build the page automatically. Nor do you need to create a separate page for each product. Just build one page, and PHP fills in the details. Other uses of PHP include creating login systems, uploading files, and sending emails. Just about every online store, news website, blog, or social networking site uses PHP or a similar server-side technology.

Depending on how it’s being used, PHP code can be embedded in a web page or stored in external files. However, unlike CSS or JavaScript, PHP code always remains on the web server. Visitors to your website never see it. All they see is the output. For example, lesson01/time.php contains the following code:

<p>The time in London is <?php 
$now = new DateTime();
$now->setTimezone(new DateTimeZone('Europe/London'));
echo $now->format('g.i a');
<p>In Los Angeles, it's <?php
$now->setTimezone(new DateTimeZone('America/Los_Angeles'));
echo $now->format('g.i a');

The PHP code is embedded in a couple of HTML paragraphs between <?php and ?> tags. Even if you don’t understand how it works, you can probably guess that this code has something to do with dates and time zones. In fact, it displays the current time in London and Los Angeles. It doesn’t matter where you are or when you load the page, as long as the server clock is set correctly, you will always get the correct time in those two cities. If you right-click to view the source code in a browser, you see only the HTML output. All the processing is done on the web server.

In this example, the PHP code does all the work itself. But in many cases, PHP acts as an intermediary to a database. The following diagram outlines the basic process.

This is what happens when a browser requests a web page that uses PHP:

  • The web server sends the page to the PHP engine—which resides on the server— for processing.
  • If the PHP script doesn’t need to communicate with the database, the PHP engine generates the HTML output, and the web server sends it back to the browser.
  • If the script needs to interact with the database—getting the results of a search, or inserting or updating data—the PHP engine communicates with the database server. When the results come back, the PHP engine puts everything together, and the web server sends the resulting web page back to the browser.

A lot goes on, but most requests take only a few microseconds, and then the web page is on its way to the browser with no perceptible delay from the user’s point of view.

PHP’s role ends as soon as the output has been sent to the browser. The time shown by time.php is fixed; it won’t update automatically a minute later. For that to happen, you need to refresh the page or create a JavaScript function to change the time within the user’s browser. If you want PHP to do something in response to user action on a web page, it involves another round trip to the server. In the past, this meant reloading the page. However, as you’ll see later in this book, you can refresh the page seamlessly by sending the request in the background and updating the content with Ajax.

Why choose PHP?

PHP isn’t the only server-side technology available. In fact, Dreamweaver has varying degrees of support for seven. Most have similar capabilities, and choosing which is the most suitable for your circumstances isn’t always easy. However, PHP has the following advantages:

  • PHP runs on Windows, Mac OS X, and Linux. With only a few minor exceptions, code written on one operating system works on any of the others.
  • It’s open source and free.
  • It’s widely available.
  • It’s relatively easy to learn.
  • There’s a large community of active users, so help is rarely far away.
  • It’s simple enough to incorporate into a small website, yet powerful enough to drive some of the busiest websites, including Facebook, Wikipedia, and Yahoo!
  • In a survey of media executives by the Society of Digital Agencies (SoDA), nearly 50 percent said they regarded PHP as an important tool for their company in 2010. The figure for ASP.NET was 32 percent. Fewer than 10 percent said they regarded Ruby on Rails as important for their company.
  • In the same survey, more than 50 percent said they would be hiring people with PHP skills in 2010. The only web-related skills in greater demand were Flash and ActionScript.

So are there any disadvantages in choosing PHP?

Comparing server-side technologies is difficult, but the main disadvantage of PHP is, paradoxically, that it’s easy to learn. Many people copy scripts from online tutorials without understanding the code, often leaving gaping security holes in their websites. PHP is as secure as any other server-side technology, and security-related bugs are usually dealt with very quickly. But just like the electricity in your house, it’s safe only insofar as it’s used and maintained correctly. Fortunately, it’s not difficult to write secure code, and there is emphasis on security throughout this book.

Which database should I choose?

More often than not, PHP is used in conjunction with MySQL, the most popular open-source database, which is fast, powerful, and well suited for use in websites. It’s the database that runs WordPress, Drupal, and Joomla! and is also used by high-traffic websites like Flickr, Facebook, and YouTube.

MySQL is currently owned by Oracle Corporation, one of the leading database software companies, but the Community Edition of MySQL is free. The functionality of the Community Edition is identical to the for-purchase Enterprise version. The only difference is that no support is offered with the free version. But that’s rarely a problem because of the active community willing to offer help online.

Like PHP, MySQL works on all the main operating systems, so you can develop on one system and later transfer your database to another. Also, most hosting companies offer PHP in combination with MySQL. For all these reasons, the combination of PHP and MySQL is used in this book.

PHP and MySQL have become so closely connected that many people think you can’t have one without the other. Unlike love and marriage in Frank Sinatra’s 1950s hit, you can have PHP without MySQL. PHP works with all the main database systems, including Microsoft SQL Server, Oracle, and PostgreSQL. You can easily adapt much of the code in later lessons to work with the database of your choice.

Peachpit Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Peachpit and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Peachpit products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by Adobe Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive:

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020