Functional Dependencies
Learn about functional dependencies and how they work.
We'll cover the following...
Imagine you’re running an online store, and one of your VIP customers—Jane Smith—moves to a new address.
She’s placed 50 orders with you over time. To update her address, you’d have to locate each of those 50 orders and change the address manually. If you overlook even one, your records become inconsistent. This is a classic example of a data management problem caused by a poorly structured database.
So, how do we prevent such issues?
The key lies in understanding how pieces of data relate to one another. In database design, this concept is formalized as a functional dependency—a foundational principle that helps us build clean, efficient, and reliable databases.
In this lesson, we will dive deep into this foundational concept. By the end, we’ll be able to:
Define what a functional dependency is and how it works.
Identify different types of functional dependencies in a table.
Explain why understanding functional dependencies is critical for designing robust databases.
Recognize how functional dependencies reveal potential design flaws.
Let’s get started and learn how to build smarter database schemas!
Functional dependency
At its core, a functional dependency is a rule or a constraint between two sets of attributes in a database table. It ensures that the value of one attribute can be uniquely determined by the value of another. Think of it as a cause-and-effect relationship within your data. If we know the value of attribute A, and it guarantees that we will know the value of attribute B, then we can say that B is functionally dependent on A.
We write this relationship as A → B, which reads as: A functionally determines B, or B is functionally dependent on A.