New Feature: Playlist Center! Pick a topic and let our playlists guide the way.

Start learning with our library of video tutorials taught by experts. Get started

PHP with MySQL Essential Training
Illustration by Don Barnett

NULL and empty


From:

PHP with MySQL Essential Training

with Kevin Skoglund

Video: NULL and empty

In this video, we're going to be talking about NULL. NULL is a fancy term for nothing, for not having a value. It's not zero. It's not an empty string. It's the actual lack of a value. And if we can set a value into a variable, we also have to have some way to talk about the fact that variable might not have a value at all. And null allows us to do that. Let's take a look at it by first creating a page where we can work with null. And I'm going to do that by opening up basic.html, and then choosing Save As. We're going to save this as null.php. So, null now, like true and false, the booleans that we just talked about. Null can either be written in lower case, or in all upper case. And you'll waste a lot of time arguing with people about the right way to do it in PHP.
Expand all | Collapse all
  1. 4m 8s
    1. Welcome
      1m 0s
    2. Using the exercise files
      3m 8s
  2. 15m 6s
    1. What is PHP?
      3m 52s
    2. The history of PHP
      2m 51s
    3. Why choose PHP?
      4m 10s
    4. Installation overview
      4m 13s
  3. 54m 53s
    1. Overview
      2m 33s
    2. Working with Apache Web Server
      6m 56s
    3. Changing the document root
      7m 24s
    4. Enabling PHP
      6m 16s
    5. Upgrading PHP
      3m 30s
    6. Configuring PHP
      10m 3s
    7. Installing MySQL
      5m 46s
    8. Configuring MySQL
      7m 24s
    9. Text editor
      5m 1s
  4. 31m 25s
    1. Overview
      3m 27s
    2. Installing WampServer
      5m 46s
    3. Finding the document root
      2m 24s
    4. Configuring PHP
      8m 12s
    5. Configuring MySQL
      5m 45s
    6. Text editor
      5m 51s
  5. 19m 12s
    1. Embedding PHP code on a page
      6m 43s
    2. Outputting dynamic text
      5m 55s
    3. The operational trail
      2m 27s
    4. Inserting code comments
      4m 7s
  6. 1h 18m
    1. Variables
      7m 50s
    2. Strings
      4m 38s
    3. String functions
      8m 54s
    4. Numbers part one: Integers
      6m 27s
    5. Numbers part two: Floating points
      5m 25s
    6. Arrays
      10m 0s
    7. Associative arrays
      6m 37s
    8. Array functions
      6m 33s
    9. Booleans
      3m 50s
    10. NULL and empty
      5m 15s
    11. Type juggling and casting
      8m 27s
    12. Constants
      4m 43s
  7. 27m 37s
    1. If statements
      6m 0s
    2. Else and elseif statements
      4m 16s
    3. Logical operators
      7m 30s
    4. Switch statements
      9m 51s
  8. 42m 15s
    1. While loops
      8m 41s
    2. For loops
      5m 59s
    3. Foreach loops
      8m 16s
    4. Continue
      8m 28s
    5. Break
      4m 8s
    6. Understanding array pointers
      6m 43s
  9. 37m 25s
    1. Defining functions
      8m 25s
    2. Function arguments
      5m 32s
    3. Returning values from a function
      7m 33s
    4. Multiple return values
      4m 53s
    5. Scope and global variables
      6m 2s
    6. Setting default argument values
      5m 0s
  10. 20m 18s
    1. Common problems
      3m 47s
    2. Warnings and errors
      8m 36s
    3. Debugging and troubleshooting
      7m 55s
  11. 57m 57s
    1. Links and URLs
      5m 33s
    2. Using GET values
      5m 35s
    3. Encoding GET values
      8m 41s
    4. Encoding for HTML
      9m 26s
    5. Including and requiring files
      7m 40s
    6. Modifying headers
      6m 45s
    7. Page redirection
      6m 43s
    8. Output buffering
      7m 34s
  12. 1h 3m
    1. Building forms
      7m 28s
    2. Detecting form submissions
      5m 59s
    3. Single-page form processing
      7m 57s
    4. Validating form values
      10m 40s
    5. Problems with validation logic
      9m 54s
    6. Displaying validation errors
      7m 23s
    7. Custom validation functions
      6m 28s
    8. Single-page form with validations
      7m 25s
  13. 28m 5s
    1. Working with cookies
      2m 49s
    2. Setting cookie values
      5m 55s
    3. Reading cookie values
      6m 1s
    4. Unsetting cookie values
      4m 51s
    5. Working with sessions
      8m 29s
  14. 48m 39s
    1. MySQL introduction
      6m 43s
    2. Creating a database
      7m 41s
    3. Creating a database table
      7m 42s
    4. CRUD in MySQL
      5m 48s
    5. Populating a MySQL database
      7m 32s
    6. Relational database tables
      6m 40s
    7. Populating the relational table
      6m 33s
  15. 56m 4s
    1. Database APIs in PHP
      4m 51s
    2. Connecting to MySQL with PHP
      7m 45s
    3. Retrieving data from MySQL
      8m 47s
    4. Working with retrieved data
      6m 12s
    5. Creating records with PHP
      6m 58s
    6. Updating and deleting records with PHP
      9m 6s
    7. SQL injection
      3m 5s
    8. Escaping strings for MySQL
      6m 45s
    9. Introducing prepared statements
      2m 35s
  16. 35m 58s
    1. Blueprinting the application
      7m 19s
    2. Building the CMS database
      5m 14s
    3. Establishing your work area
      4m 38s
    4. Creating and styling the first page
      4m 22s
    5. Making page assets reusable
      6m 36s
    6. Connecting the application to the database
      7m 49s
  17. 32m 49s
    1. Adding pages to the navigation subjects
      5m 58s
    2. Refactoring the navigation
      6m 7s
    3. Selecting pages from the navigation
      6m 2s
    4. Highlighting the current page
      5m 26s
    5. Moving the navigation to a function
      9m 16s
  18. 1h 45m
    1. Finding a subject in the database
      9m 48s
    2. Refactoring the page selection
      10m 52s
    3. Creating a new subject form
      6m 55s
    4. Processing form values and adding subjects
      11m 20s
    5. Passing data in the session
      9m 16s
    6. Validating form values
      9m 40s
    7. Creating an edit subject form
      8m 30s
    8. Using single-page submission
      7m 44s
    9. Deleting a subject
      9m 44s
    10. Cleaning up
      10m 37s
    11. Assignment: Pages CRUD
      4m 30s
    12. Assignment results: Pages CRUD
      6m 10s
  19. 39m 26s
    1. The public appearance
      8m 52s
    2. Using a context for conditional code
      11m 37s
    3. Adding a default subject behavior
      6m 9s
    4. The public content area
      5m 51s
    5. Protecting page visibility
      6m 57s
  20. 1h 3m
    1. User authentication overview
      4m 3s
    2. Admin CRUD
      8m 41s
    3. Encrypting passwords
      7m 26s
    4. Salting passwords
      5m 42s
    5. Adding password encryption to CMS
      11m 54s
    6. New PHP password functions
      3m 13s
    7. Creating a login system
      11m 28s
    8. Checking for authorization
      5m 48s
    9. Creating a logout page
      5m 40s
  21. 2m 4s
    1. Next steps
      2m 4s

Watch this entire course now—plus get access to every course in the library. Each course includes high-quality videos taught by expert instructors.

Become a member
please wait ...
PHP with MySQL Essential Training
14h 24m Beginner Jun 04, 2013

Viewers: in countries Watching now:

PHP is a popular, reliable programming language at the foundation of many smart, data-driven websites. This comprehensive course from Kevin Skoglund helps developers learn the basics of PHP (including variables, logical expressions, loops, and functions), understand how to connect PHP to a MySQL database, and gain experience developing a complete web application with site navigation, form validation, and a password-protected admin area. Kevin also covers the basic CRUD routines for updating a database, debugging techniques, and usable user interfaces. Along the way, he provides practical advice, offers examples of best practices, and demonstrates refactoring techniques to improve existing code.

Topics include:
  • What is PHP?
  • Installing and configuring PHP and MySQL
  • Exploring data types
  • Controlling code with logical expressions and loops
  • Using PHP's built-in functions
  • Writing custom functions
  • Building dynamic webpages
  • Working with forms and form data
  • Using cookies and sessions to store data
  • Connecting to MySQL with PHP
  • Creating and editing database records
  • Building a content management system
  • Adding user authentication
Subjects:
Developer Servers Programming Languages Web Development
Software:
MySQL PHP
Author:
Kevin Skoglund

NULL and empty

In this video, we're going to be talking about NULL. NULL is a fancy term for nothing, for not having a value. It's not zero. It's not an empty string. It's the actual lack of a value. And if we can set a value into a variable, we also have to have some way to talk about the fact that variable might not have a value at all. And null allows us to do that. Let's take a look at it by first creating a page where we can work with null. And I'm going to do that by opening up basic.html, and then choosing Save As. We're going to save this as null.php. So, null now, like true and false, the booleans that we just talked about. Null can either be written in lower case, or in all upper case. And you'll waste a lot of time arguing with people about the right way to do it in PHP.

And whether one is better than the other, or one has better performance than the other. The truth is that they're case insensitive and that you can use absolutely whichever one you prefer. There is no difference. I'm going to use the lower case version. And let's set a variable equal to var1 equal to null. And just for contrast, let's set var2 equal to an empty string. Just so that we can see the difference between those two. Now, like a lot of the other types that we've looked at, there are functions that allow us to test whether it is of a certain type. So, we can test whether this is null or not.

is_null will tell us if the variable is null, and we'll do that to both of these. Let's also do it to a third one as well. Make this var3, then we'll test var3. Now, var3 isn't set, right? It hasn't been set to anything, so we'll see what that gives us back. So we return to Firefox, and set up Booleans. We'll load it up null.php. So, it came back and said is variable 1 null? Yes, it is. Variable 2, is that null? No, it's not. That was my empty string. So, that's not considered null. var3, is it null? I get a notice here that's not an error. That's not a warning.

It's a notice just saying hey, level heads up here, you're in the middle of developing. And I noticed that you're making a reference to an undefined variable so I want to call your attention to it here. Note that these are different than, than warnings in PHP. But it goes ahead after that notice and gives us the result, which is the yes in fact, var3 is null. The fact that it hasn't been set means that it has no value. So, the answer is true, it is null. So, notice the difference between that. Notice what happened with var1 and what happened with var3. By setting it specifically to null, I avoid this notice that pops up.

And we can contrast that with what happens if we have is set. Alright, so let me just paste in a few others here. var1 is set, var2 is set, or var3 is set. Is set doesn't have a, a space here, no underscore between is set, it's all run together. And let's just reload the page now. And you can see that it tells us that var1 is not set, var3 is not set, and var2 is set. Now, not set means that it's null, right? So being null, we're being told, is the same thing as being unset. Now, we know it's not exactly the same thing.

We saw that with is_null. But it's close. For the purposes of most of our tests, it will be the same. So that's what null is, null is just the lack of having a value. That's a pretty easy concept. But I think this is also a good spot for us to talk about a function in PHP called Empty. And as you would expect, empty returns a boolean, true or false, for whether a variable is considered to be empty. What you might not expect though, are the things that it considers to be empty. In PHP, empty is going to be an empty string, null, 0, 0.0. Meaning, a float in which the value is zero, a string with a zero inside of it, false, or an empty array.

All of those things are considered empty. So, we can provide our test again here, for whether these things are considered empty. And let's define var3 here, just so it has a value. var3, it's got a dollar sign in front. var3 is going to be equal to, let's make it zero inside the string, like that. Let's go back over to our browser and let's try this out. And let's see what things are empty. Is var1 empty? Yes. var2 empty? Yes. var3 is empty also. So null, an empty string.

And this is a very important one, 0 inside the string are all considered to be empty. Now, this broad, catch all approach can be extremely useful, but you have to use it with a lot of caution. For example, imagine that you had a web form that was submitting a value to your PHP code. And imagine that, that field was, how many children do you have? You want to check if that field is left blank by the user. And if not, you want to say hey, you need to fill out this. I need to know how many children you have. Empty would detect an empty string or no value being submitted, which is what you want.

But it would also not allow the number of children you have to be zero as a value. Which is probably not what you intended, right? They would not be able to submit the value of zero. Just like we saw here, that would be considered empty as well. So most times, you'll need to use further conditions with empty such as, is it empty and also not numeric? Or is it empty but not null? Now, I'm mentioning this now because empty is a leading cause of bugs in PHP code. So, something you're really going to want to keep an eye out for.

Find answers to the most frequently asked questions about PHP with MySQL Essential Training.


Expand all | Collapse all
please wait ...
Q: This course was revised on 6/4/2013. What changed?
A: The old version of this course was 6 years old and it was time for a complete revision, using PHP 5.4. (The tutorials will work with any version of PHP and covers any differences you might encounter). The author has also added updated installation instructions for Mac OS X Mountain Lion and Windows 8. The topics and end project are the same, but the code is slightly different. It also addresses frequently asked questions from the previous version.
 
Share a link to this course

What are exercise files?

Exercise files are the same files the author uses in the course. Save time by downloading the author's files instead of setting up your own files, and learn by following along with the instructor.

Can I take this course without the exercise files?

Yes! If you decide you would like the exercise files later, you can upgrade to a premium account any time.

Become a member Download sample files See plans and pricing

Please wait... please wait ...
Upgrade to get access to exercise files.

Exercise files video

How to use exercise files.

Learn by watching, listening, and doing, Exercise files are the same files the author uses in the course, so you can download them and follow along Premium memberships include access to all exercise files in the library.
Upgrade now


Exercise files

Exercise files video

How to use exercise files.

For additional information on downloading and using exercise files, watch our instructional video or read the instructions in the FAQ.

This course includes free exercise files, so you can practice while you watch the course. To access all the exercise files in our library, become a Premium Member.

join now Upgrade now

Are you sure you want to mark all the videos in this course as unwatched?

This will not affect your course history, your reports, or your certificates of completion for this course.


Mark all as unwatched Cancel

Congratulations

You have completed PHP with MySQL Essential Training.

Return to your organization's learning portal to continue training, or close this page.


OK
Become a member to add this course to a playlist

Join today and get unlimited access to the entire library of video courses—and create as many playlists as you like.

Get started

Already a member?

Become a member to like this course.

Join today and get unlimited access to the entire library of video courses.

Get started

Already a member?

Exercise files

Learn by watching, listening, and doing! Exercise files are the same files the author uses in the course, so you can download them and follow along. Exercise files are available with all Premium memberships. Learn more

Get started

Already a Premium member?

Exercise files video

How to use exercise files.

Ask a question

Thanks for contacting us.
You’ll hear from our Customer Service team within 24 hours.

Please enter the text shown below:

The classic layout automatically defaults to the latest Flash Player.

To choose a different player, hold the cursor over your name at the top right of any lynda.com page and choose Site preferencesfrom the dropdown menu.

Continue to classic layout Stay on new layout
Exercise files

Access exercise files from a button right under the course name.

Mark videos as unwatched

Remove icons showing you already watched videos if you want to start over.

Control your viewing experience

Make the video wide, narrow, full-screen, or pop the player out of the page into its own window.

Interactive transcripts

Click on text in the transcript to jump to that spot in the video. As the video plays, the relevant spot in the transcript will be highlighted.

Are you sure you want to delete this note?

No

Notes cannot be added for locked videos.

Thanks for signing up.

We’ll send you a confirmation email shortly.


Sign up and receive emails about lynda.com and our online training library:

Here’s our privacy policy with more details about how we handle your information.

Keep up with news, tips, and latest courses with emails from lynda.com.

Sign up and receive emails about lynda.com and our online training library:

Here’s our privacy policy with more details about how we handle your information.

   
submit Lightbox submit clicked
Terms and conditions of use

We've updated our terms and conditions (now called terms of service).Go
Review and accept our updated terms of service.