What is Unique Key in DBMS? Functions, Uses, and How It Works

A unique key is an essential element in a database management system (DBMS) that is used to uniquely identify each row of data in a table. Its main function is to ensure that there is no duplication of values in a column that has been designated as a unique key.

Without a unique key, the database is at risk of having the same data more than once. This can lead to data inconsistencies and inaccuracies.

Understand more about unique keys through this article. You will learn how they work, their functions, and examples of their use.

Related Read: 7 Types of Database Keys and Their Functions

What is a Unique Key?

A unique key is one of several types of keys in database management systems. These types of keys serve to ensure that there are no duplicate values in a column. This key plays a very important role in maintaining the integrity and uniqueness of data.

The unique keys provide strict control over value entry, keeping each record in a database table unique. A unique key has several characteristics, including allowing only one null value and being assignable to one or more columns in a table.

Appropriate conditions for using a unique key include:

• When identifying each row of data must be unique.
• When tables need a relationship that depends on the uniqueness of the data.
• If certain data has a high risk of duplication and is critical to the business.

How Unique Keys Works

The way a unique key works is similar to setting limits to ensure that values entered in a column are always unique and none can be repeated.

When entering data, the system validates the values against existing ones. If there is an attempt to enter a value that already exists, the system will reject the data insertion to prevent duplication.

Also Read: Primary Key in Database Management System (DBMS)

Unique Keys’ Function

Unique keys have several very important functions in database management. Here are some of them:

1. Ensure data uniqueness
   A unique key ensures that all data in a column remains distinct from each other. This implementation is crucial in preventing data duplication, which can not only compromise database integrity but also cause problems when querying.
2. Be a reference for other tables
   Unique keys do not limit their role to one table; they also serve as references to other tables, forming strong relationships. The uniqueness of the data provides an efficient ability to build connections between tables, which is very useful for complex data integration.
3. Improve query performance
   By ensuring that each value in a column is unique, a unique key can increase efficiency when searching for data. A unique key facilitates a faster and more precise search process in a database.
4. Makes searching easier
   The unique keys make the process of searching and retrieving data easier. Users or systems can easily find the desired data row without worrying about duplicate values that slow down data retrieval.

#1. Example of Using Unique Keys

When using unique keys, it is important to ensure that the column used as a unique key does not contain duplicate values. Additionally, understanding the data structure in the column is crucial to avoid disrupting database performance.

You can see an example of unique keys in the e-commerce table that manages product data. A ‘product_code’ column can be used as a unique key so that each product has a unique code that can be clearly identified. In the SQL system, the implementation can be as follows:

CREATE TABLE products (
    id INT PRIMARY KEY,
    product_code VARCHAR(255) UNIQUE,
    product_name VARCHAR(255),
    price DECIMAL
);

Another Example of Using a Unique Key in DBMS

Let’s consider a student database at a university. Each student has a Student ID (which is a unique identification number) that distinguishes them from all other students. This Student ID is an excellent example of unique keys because it ensures that no two students have the same ID.

Also Read: MySQL DROP All Tables | 5 Ways to DROP All Tables

Why Use a Unique Key for Student Data?

Imagine a situation where two students accidentally have the same Student ID in the system. This would cause confusion when managing student records—such as grading, course enrollment, or even issuing diplomas—because the system wouldn’t be able to tell which student is which.

How the Unique Key Works in This Example:

In the student database, the Student ID column is set as a unique key. Here’s how it works:

1. When a new student is enrolled, the database checks if their Student ID already exists in the system.
2. If the Student ID is already used by another student, the system will reject the entry to avoid duplication.
3. If the Student ID is not yet in use, the system will accept the new record, ensuring that every student has a distinct and unique identity in the database.

Here’s an example of how it might look in SQL:

CREATE TABLE students (
    student_id INT UNIQUE,
    first_name VARCHAR(255),
    last_name VARCHAR(255),
    email VARCHAR(255)
);

In this table:

• The student_id column is a unique key, meaning no two students can have the same ID.
• Even if two students have the same first or last name, their student_id will always be different, which avoids confusion.

Also Read: MySQL Data Types – a complete list

Why Is This Important?

Unique keys help the university keep its data clean and organized. If the same student ID is assigned to multiple students, it would lead to errors, making it difficult to manage records efficiently.

In summary, by using a unique key like Student ID, the university ensures that each student is uniquely identifiable, which simplifies everything from course registration to grading and beyond.

Do You Know What a Unique Key Is?

So, a unique key is a key element that ensures the uniqueness of data in a database management system and increases its efficiency. The presence of unique keys ensures the uniqueness of the values in the column so that there is no duplication.

The main function of unique keys lies in their ability to increase integrity and strengthen relationships between data. Some of the main characteristics of a unique key include its ability to maintain data uniqueness and serve as a reference between tables. If you want the Official MySQL Documentation on Constraints, you can visit here.