Master Facebook SQL Interview Questions: Unlock Your Dream Data Role

Cracking the SQL coding challenges is a crucial step in securing your dream data role at Facebook (Meta). With the company’s emphasis on data-driven decision-making, mastering SQL is an essential skill for roles like Data Analyst, Data Scientist, and Data Engineer. In this comprehensive guide, we’ll explore the most frequently asked Facebook SQL interview questions, providing you with the knowledge and practice you need to excel.

Understanding the Importance of SQL at Facebook

Facebook (Meta) is a data-driven company that heavily relies on SQL for various data operations and analysis. From tracking user engagement and advertising metrics to optimizing product features and making informed business decisions, SQL plays a pivotal role in Facebook’s operations. As a result, proficiency in SQL is a critical requirement for many data-related roles within the company.

Frequently Asked Facebook SQL Interview Questions

Based on our analysis of recent Facebook interviews and the company’s recommendations, we’ve curated a list of the most commonly asked SQL interview questions. These questions will test your SQL knowledge, problem-solving abilities, and coding skills, ensuring you’re well-prepared for the challenges ahead.

1. Average Post Hiatus

Given a table of Facebook posts, for each user who posted at least twice in a specific year, write a SQL query to find the number of days between each user’s first post of the year and last post of the year. Output the user and the number of days between their first and last posts.

-- SolutionSELECT user_id, MAX(post_date) - MIN(post_date) AS days_betweenFROM postsWHERE EXTRACT(YEAR FROM post_date) = 2024GROUP BY user_idHAVING COUNT(DISTINCT post_date) > 1;

2. Facebook Power Users

Write a SQL query to return the IDs of all Facebook power users, along with the number of posts and the average number of reactions per post. A power user is defined as someone who posts at least twice a day and receives an average of 150 comments and/or reactions per post.

-- SolutionWITH post_count AS (  SELECT user_id, COUNT(*) AS num_posts  FROM user_posts  GROUP BY user_id),avg_reactions AS (  SELECT user_posts.user_id, AVG(post_interactions.comments + post_interactions.reactions) AS avg_reactions  FROM user_posts  JOIN post_interactions ON user_posts.post_id = post_interactions.post_id  GROUP BY user_posts.user_id)SELECT post_count.user_id, num_posts, avg_reactionsFROM post_countJOIN avg_reactions ON post_count.user_id = avg_reactions.user_idWHERE num_posts >= 2 * (SELECT COUNT(DISTINCT post_date) FROM user_posts)  AND avg_reactions >= 150;

3. Active User Retention

Assume you’re given a table containing information on Facebook user actions. Write a SQL query to obtain the number of monthly active users (MAUs) in a specific month, including the month in numerical format. An active user is defined as someone who has performed actions such as ‘sign-in’, ‘like’, or ‘comment’ in both the current month and the previous month.

-- SolutionWITH current_month AS (  SELECT user_id  FROM user_events  WHERE EXTRACT(MONTH FROM event_date) = 7 AND EXTRACT(YEAR FROM event_date) = 2022  GROUP BY user_id),prev_month AS (  SELECT user_id  FROM user_events  WHERE EXTRACT(MONTH FROM event_date) = 6 AND EXTRACT(YEAR FROM event_date) = 2022  GROUP BY user_id)SELECT 7 AS month, COUNT(*) AS monthly_active_usersFROM current_monthJOIN prev_month ON current_month.user_id = prev_month.user_id;

4. Facebook Friend Recommendations

Facebook wants to recommend new friends to people who show interest in attending two or more of the same private Facebook events. Write a SQL query to find pairs of users who are not friends but have shown interest in attending two or more of the same private events.

-- SolutionWITH interested_users AS (  SELECT user_id, event_id  FROM event_attendance  WHERE attendance_status IN ('going', 'maybe')    AND event_type = 'private')SELECT DISTINCT a.user_id AS user_a_id, b.user_id AS user_b_idFROM interested_users aJOIN interested_users b ON a.event_id = b.event_id AND a.user_id < b.user_idJOIN friend_relationships fr ON a.user_id = fr.user_a_id AND b.user_id = fr.user_b_idWHERE fr.status = 'not_friends'GROUP BY a.user_id, b.user_idHAVING COUNT(DISTINCT a.event_id) >= 2;

5. Average Number of Shares per Post

As a data analyst at Facebook, you are asked to find the average number of shares per post for each user. Write a SQL query to find the average number of shares per post for each user.

-- SolutionSELECT user_posts.user_id, COALESCE(AVG(shares.share_count), 0) AS avg_shares_per_postFROM user_postsLEFT JOIN (  SELECT post_id, COUNT(*) AS share_count  FROM post_shares  GROUP BY post_id) shares ON user_posts.post_id = shares.post_idGROUP BY user_posts.user_id;

6. Calculate Facebook Ad Click-Through Rate

Write a SQL query to calculate the click-through rate (CTR) for the Facebook app in a specific year, rounded to two decimal places. The CTR is defined as the percentage of clicks divided by the number of impressions.

-- SolutionWITH clicks AS (  SELECT app_id, COUNT(*) AS num_clicks  FROM app_events  WHERE event_type = 'click' AND EXTRACT(YEAR FROM timestamp) = 2022  GROUP BY app_id),impressions AS (  SELECT app_id, COUNT(*) AS num_impressions  FROM app_events  WHERE event_type = 'impression' AND EXTRACT(YEAR FROM timestamp) = 2022  GROUP BY app_id)SELECT c.app_id, ROUND(100.0 * num_clicks / num_impressions, 2) AS ctrFROM clicks cJOIN impressions i ON c.app_id = i.app_id;

Preparation Tips for Facebook SQL Interviews

In addition to practicing the SQL interview questions provided, here are some tips to help you prepare effectively for your Facebook SQL interview:

• Understand SQL Fundamentals: Ensure you have a solid grasp of SQL concepts such as joins, subqueries, aggregations, and window functions. Facebook interviews often test these fundamental concepts.

• Practice with Real-World Datasets: While practicing SQL questions, try to work with datasets that resemble real-world scenarios. This will help you develop problem-solving skills and prepare for the types of challenges you may encounter in a professional setting.

• Learn Advanced SQL Techniques: Familiarize yourself with advanced SQL techniques like recursive queries, common table expressions (CTEs), and pivoting/unpivoting data. These techniques may be required for solving complex problems during the interview.

• Optimize Your Queries: Pay attention to query optimization techniques, such as indexing, partitioning, and query rewriting. Efficient queries are highly valued at Facebook and other tech companies.

• Practice Coding on a Whiteboard or Text Editor: During the interview, you may be asked to write SQL queries on a whiteboard or in a text editor. Practice this skill to ensure you can communicate your thought process effectively and write clean, readable code.

• Understand Data Modeling: Gain a basic understanding of data modeling concepts, such as normalization and denormalization. These concepts may come into play when designing or working with complex database schemas.

• Stay Updated with Industry Trends: Keep yourself informed about the latest trends, technologies, and best practices in the data analytics and database management fields. This will demonstrate your passion for the field and your commitment to continuous learning.

Remember, successful interview preparation requires dedication, practice, and a solid understanding of both technical and non-technical aspects. By combining your SQL coding skills with industry knowledge and effective communication, you’ll be well-equipped to impress the Facebook interview panel and increase your chances of landing your dream data role.

Good luck with your Facebook SQL interview preparation!