602. Friend Requests II: Who Has the Most Friends | SQL | LeetCode |

Опубликовано: 13 Февраль 2025
на канале: SheCodes

🔍 LeetCode SQL Problem Explained: Friend Requests II - Who Has the Most Friends? 🔍

Welcome back to She Codes! In today's video, we’re diving into an intriguing LeetCode SQL problem that’s all about friendships and counting connections! 🎉 If you've ever wondered how to identify the person with the most friends in a social network database, you're in the right place. We’ll be solving LeetCode Problem 602: Friend Requests II: Who Has the Most Friends?

📚 Problem Overview:
We have a table called RequestAccepted, which records friend requests between users. The table tracks:

requester_id: the person sending the friend request,
accepter_id: the person accepting the friend request,
accept_date: when the request was accepted.
Our task? Find the person with the most friends. Sounds simple, right? Well, it's all about using SQL queries to combine information and count the number of unique friends for each user. But, there’s a twist – in a real-world situation, there might be more than one person with the same number of friends! So, how do we handle that? We’ll walk you through the process step by step. 🧑‍💻

🛠️ SQL Concepts Used:
UNION ALL: Combining data from two columns (requester_id and accepter_id) to create a complete list of all friendships.
COUNT Function: To calculate how many friends each user has.
GROUP BY: To organize the data by user ID and tally their friendships.
Common Table Expressions (CTE): We’ll use a CTE to keep our query clean and readable by separating the logic into manageable parts.
ORDER BY and LIMIT: To find the user with the maximum number of friends.
🧩 Step-by-Step Breakdown:
Combining Friendships: We start by merging the requester_id and accepter_id columns to get a comprehensive list of all users involved in friendships.

Counting Friends: Using SQL's COUNT function, we group friendships by each user ID and calculate how many friends each person has.

Identifying the Person with the Most Friends: Finally, we use MAX to find the user with the highest number of friends. The query will return the person who has the most unique friendships.

💡 Real-World Scenario:
Imagine you're building a social network platform like Facebook or LinkedIn, where you need to generate user statistics to see who has the most connections. This query is a practical way to handle such data and derive insights that could be useful for ranking, recommendations, or even personalized features!

🎯 Why This Problem Matters:
It teaches you how to work with relationship data in SQL, a common task when dealing with databases in social networks, customer relationship management (CRM) systems, or any application where users interact with each other.
You’ll also learn how to optimize SQL queries for scenarios with large datasets.
📌 Bonus Tip: I also discuss how to handle cases where multiple users have the same number of friends – an important consideration when designing real-world systems!

If you’re looking to sharpen your SQL skills, especially for LeetCode, this video is perfect for you. Let’s tackle this problem together! 💪

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