Search icon CANCEL
Subscription
0
Cart icon
Your Cart (0 item)
Close icon
You have no products in your basket yet
Arrow left icon
Explore Products
Best Sellers
New Releases
Books
Videos
Audiobooks
Learning Hub
Conferences
Free Learning
Arrow right icon
Arrow up icon
GO TO TOP
Learning PHP 7

You're reading from   Learning PHP 7 Build powerful real-life web applications in a simple way using PHP7 and its ecosystem.

Arrow left icon
Product type Paperback
Published in Mar 2016
Publisher Packt
ISBN-13 9781785880544
Length 414 pages
Edition 1st Edition
Languages
Tools
Arrow right icon
Author (1):
Arrow left icon
Antonio L Zapata (GBP) Antonio L Zapata (GBP)
Author Profile Icon Antonio L Zapata (GBP)
Antonio L Zapata (GBP)
Arrow right icon
View More author details
Toc

Table of Contents (12) Chapters Close

Preface 1. Setting Up the Environment 2. Web Applications with PHP FREE CHAPTER 3. Understanding PHP Basics 4. Creating Clean Code with OOP 5. Using Databases 6. Adapting to MVC 7. Testing Web Applications 8. Using Existing PHP Frameworks 9. Building REST APIs 10. Behavioral Testing Index

Keys and constraints


Now that we have our main tables defined, let's try to think about how the data inside would look. Each row inside a table would describe an object, which may be either a book or a customer. What would happen if our application has a bug and allows us to create books or customers with the same data? How will the database differentiate them? In theory, we will assign IDs to customers in order to avoid these scenarios, but how do we enforce that the ID not be repeated?

MySQL has a mechanism that allows you to enforce certain restrictions on your data. Other than attributes such as NOT NULL or UNSIGNED that you already saw, you can tell MySQL that certain fields are more special than others and instruct it to add some behavior to them. These mechanisms are called keys, and there are four types: primary key, unique key, foreign key, and index. Let's take a closer look at them.

Primary keys

Primary keys are fields that identify a unique row from a table. There cannot be two...

lock icon The rest of the chapter is locked
Register for a free Packt account to unlock a world of extra content!
A free Packt account unlocks extra newsletters, articles, discounted offers, and much more. Start advancing your knowledge today.
Unlock this book and the full library FREE for 7 days
Get unlimited access to 7000+ expert-authored eBooks and videos courses covering every tech area you can think of
Renews at $19.99/month. Cancel anytime
Banner background image