One of the **key characteristics** of a **set** is that it does not allow **duplicate values**. When you add a **new element** to a set, if the element **already exists**, it won't be added again.

Sets are commonly used for storing **unique values**, such as **user IDs**, **IP addresses**, or any other data where **duplicates** must be avoided.

# Basic Commands for Working with Sets

Redis **sets** come with several **commands** that make it easy to **add**, **remove**, and **check elements**

### Adding and Removing Elements

The `SADD` command **adds elements** to a set, **ignoring duplicates**, and the `SREM` command **removes elements** from a set.

```
SADD users "user1" "user2"  # adds "user1" and "user2" to the users set
SREM users "user1"  # removes "user1" from the users set
```

### Checking for an Element and Retrieving All Elements

To **check** if a specific **element** is in a set, use the `SISMEMBER` command, which returns **1** if the element is **present** and **0** if it's **not**. To get **all elements** of the set, use the `SMEMBERS` command.

```
SISMEMBER users "user2"  # checks if "user2" is in the users set (returns 1 or 0)
SMEMBERS users  # returns all elements of the users set
```

### Getting Information About the Set

To get the **number of elements** in a set, use the `SCARD` command, which returns the **number of elements** in the set.

```
SCARD users  # returns the number of elements in the users set
```

### Operations with Multiple Sets

When working with **multiple sets**, you can use the commands `SDIFF`, `SINTER`, and `SUNION` — `SDIFF` returns **elements** that are in one set but **not** in the others, `SINTER` finds **common elements** across all specified sets, and `SUNION` returns the **union** of all elements from multiple sets.

```
SDIFF set1 set2  # returns elements that are in `set1` but not in `set2`
SINTER set1 set2  # returns common elements between `set1` and `set2`
SUNION set1 set2  # returns the union of elements from `set1` and `set2`
```

What does the `SADD` command do in Redis?

Which command should you use to retrieve all elements from a set?

This course will introduce you to the fundamentals of Redis and its use in real-world applications. We'll cover key Redis commands, data types, key expiration and transactions, as well as how to integrate Redis with Spring for efficient data caching.

This section provides an introduction to Redis, highlighting its core features and common use cases. You’ll learn how to install Redis on different platforms, including Windows and macOS, and get familiar with the basics of connecting to and starting the Redis server.

Here, we explore the essential Redis commands for managing and manipulating data effectively. You'll learn how to set, retrieve, increment, and delete data using commands like SET, GET, EXISTS, INCR, DECR, and tackle practical tasks to apply these concepts in real-world scenarios.

Here, you will learn about key Redis data types, including Lists, Sets, Sorted Sets, and Hashes. You will explore their functionality and practical applications through focused exercises designed to reinforce your understanding of each data type.

You'll explore advanced features of Redis, including managing key lifecycles, executing transactions, and leveraging the Pub/Sub messaging system. Additionally, you'll learn essential security practices to safeguard your Redis environment against unauthorized access.

This section introduces the fundamentals of caching and demonstrates how to configure Redis as a cache in a Spring application. It covers key caching annotations and practical examples of caching queries in web applications, concluding with a summary of the main concepts.

Introduction to Redis

Set

Practical Use of Sets in Redis

Basic Commands for Working with Sets

Adding and Removing Elements

Checking for an Element and Retrieving All Elements

Getting Information About the Set

Operations with Multiple Sets

1. What does the `SADD` command do in Redis?

2. Which command should you use to retrieve all elements from a set?