SQL Interview at FAANG: an overview

Last updated: Nov. 9, 2023
8 mins read
Leon Wei
Leon

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Summary

Let me walk you through a typical SQL interview at one of the top tech firms, so you can get a sense of how a SQL interview is conducted and what the main criteria are to determine your performance. I will also share a few tips and techniques to give you an edge for your next interview. 


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Introduction

SQL and its related database management system, such as Hive, BigQuery, Spark SQL, are the #1 toolset in managing and processing data in the industry. If you are interviewing for a data-related job, you need to prove your SQL proficiency.

Here is a list of typical roles that will require at least one round of SQL interviews:

  1. Data analyst
  2. Data scientist
  3. Data engineer
  4. Business intelligence engineer
  5. Product analyst
  6. Decision scientist
  7. Research scientist
  8. Software engineer (especially those on the backend side)

Why is an SQL interview important for a candidate?

SQL Interview can sometimes bear other names such as Technical Data Interview or Data Processing Interview. The primary purpose is to make sure a candidate is hands-on with data and can contribute immediately after joining the company.

You will be asked to perform a series of SQL coding exercises to extract facts or insights from the given data and answer follow-up questions based on different scenarios.

I have been using SQL for 10+ years, and it is still my #1 choice in preparing data.

However, I have interviewed so many candidates who started their job searches without a solid coding skill in SQL. In the end, the SQL skills gap cost their dream jobs.

How is a SQL interview conducted?

Before COVID-19, a typical interview process included 2 or 3 rounds of phone screens and a final round of onsite interviews.

Nowadays, most of the interviews are online, often assisted by video conferencing tools such as Zoom, Webex, or Google Hangout.

In the old days, during a final interview. a candidate would be asked to write their SQL code on a whiteboard without any help from a modern IDE for syntax highlighting or auto-completion.

Nowadays, the whiteboard has been replaced by interactive online coding tools such as coderpad or google docs.

Tips: Before your interview, make sure you familiarize yourself with those online coding environments. If you don't know what tool they use, ask your recruiter.

Right before the interview, you will receive a link that points to an online coding environment, where you will code up solutions in SQL.

An interviewer will be able to see everything you type in real-time.

Create your free SQLPad account and start practicing 80 SQL interview questions online.


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A typical SQL interview process

Let's assume you are interviewing for major music streaming company (e.g., Spotify) for a data scientist role.

You are given 3 (simplified) tables:

TABLE 1: song

-- id: BIGINT
-- name: VARCHAR(255)
-- artist_id: BIGINT

The first table is a list of songs and their metadata, song names, and associated artists.

 

TABLE 2: artist 

-- id: BIGINT
-- name: VARCHAR(255)

The second table is simply an artist table with only 2 columns: artist id and the artist name.

 

TABLE 3:  daily_plays

-- date: DATE
-- country: VARCHAR(2) ('uk','us','in','jp','cn')
-- song_id BIGINT
-- plays BIGINT

The 3rd table is a daily aggregate table that counts the number of times a song is played in a country.

 

And you are asked the following questions:

Question 1: 

Write a query to return the top 5 songs in the UK yesterday.

Tips: a common mistake a beginner usually makes is diving into coding right away without fully understanding the question.

An interviewer will often start with a vague question to see if a candidate is good at communicating.

It is crucial to pause before diving into coding directly. For this question, you should clarify the following:

1. What do you mean by 'top'? What is the top's definition, number of plays, number of unique customers,  or perhaps other metrics?

2. What columns should I return, a song id, or include a song's name?

3. What if there are ties? Should I return only 1 row or all of them? (optionally)

4. Should we care about the timezone?

After clarifying this question, you can go ahead and start coding, and here is a sample solution:

 

SELECT 
    S.song_id, 
    S.name
FROM song_plays P
INNER JOIN song S
ON P.song_id = S.id
WHERE P.country = 'UK'
AND P.date = CURRENT_DATE - 1
ORDER BY daily_plays DESC
LIMIT 5;

 

Question 2: 

Write a query to return the top 5 artists in the US and UK yesterday

This question tries to evaluate whether a candidate knows window functions.

Window functions are asked a lot, especially if the hiring company has a global business. To identify top artists/songs/albums across different countries, you need to know WINDOW functions. Especially  ROW_NUMBER and RANK functions.

I’ve written an article that summarizes 4 types of window functions. Feel free to check it out, and practice some coding questions. 

SQL Window Functions
 

Again, before start coding,  try to clarify a few things with the interviewer:

1. Definition of 'top.'

2. Columns to return.

3. Situations when there are ties.

4. This is probably subtle, but because multiple artists can perform a song, you need to talk to the interviewer about how to 'count' the plays properly. For simplicity, let's assume a song only has one artist.

And here is a sample solution.

WITH artist_ranking AS (
    SELECT 
        A.artist_id,
        MAX(A.artist_name) AS artist_name,
        MAX(P.country) AS country
        ROW_NUMBER() OVER(PARTITION BY country ORDER BY SUM(plays) DESC) AS ranking
    FROM daily_plays P
    INNER JOIN song S
    ON P.song_id = S.id
    INNER JOIN artist A ON 
    A.artist_id = S.artist_id
    WHERE P.country IN ('UK', 'US')
    AND P.date = CURRENT_DATE - 1
    GROUP BY A.artist_id
) 
SELECT artist_id, artist_name, country, ranking
FROM artist_ranking
WHERE ranking <= 5
LIMIT 5;

 

At this step, if you completed the above 2 questions, the interview will have a good sense that you are very good with SQL coding.  He will likely pause SQL coding and transition to follow-up analytics questions.

Sample analytics question #1: Taylor Swift is a popular artist, but her songs' plays dropped yesterday. How would you go bout analyzing this, what data will you use, and your process?

For this kind of question (data change: drop/increase), I have created a framework that you can borrow:

1. Clarifying the question

  1. What do you mean dropped, comparing today’s data with yesterday's or same day last week?
  2. Does it drop a lot? If it only dropped a little, maybe we don't have to worry about it?

And you were told by the interviewer, it's comparing yesterday to the day before, and yes, it indeed dropped a lot significantly.

2. Rule out technical issues first

In my 15 years of career, the #1 data quality issue is often a technical issue, e.g., power outage, a bug in our logging code, someone checked in a code without testing, forgot to pay a license fee, and the third-party software stopped working. 

3. Whether it is a big deal.

Even it is a significant drop. We still don’t know whether, e.g., it could be because of seasonality, and the day before yesterday was  New Years' Day, so of course it will drop, and all other artists' songs are also dropped significantly.

And you were told by the interviewer, yes, it is a big problem, and it is not due to seasonality, and it only happened to Taylor.

4. Dive into data

After ruling out those potential issues, now it's time to dive into data.

4.1 Start with internal data (data that you already have full access to).

We can slice Taylor's song plays by different countries, genres, devices, iOS vs. Android, Web vs. Mobile, etc.  And it could be because of a particular country, we just lost a popular song's license in that country to a competitor, for example.

4.2 external data (might take extra time/resource to obtain)

Finally, you can also mention external data impact, e.g., a competitor such as Amazon Music just had a new product launch. They are giving out free listening to all Taylor's songs. 

Maybe it is because this artist dropped out of a top chart on Billboard or posted something controversial on social media. 


instamentor.com | what a typical sql interview looks like at a FAANG company

A few follow-up questions for your reference.

This round of interviews is finished at this step, and the next interviewer is waiting to join the conversation, good job!

But here are a few bonus questions for your reference, in case you want to continue practicing.

  1. Write a query to find the top trending artist.
  2. How would you design a system to identify trending artists?
  3. We want to expand our music streaming services to a few more countries. Can you help find which new countries we should add our services to? What data will you use, and why?
  4. How would you design a HOT 100 artist chart?

Tips: Many tech companies really care about how quickly they can launch the first version for system design questions. Bias towards action, and as Reid Hoffman famously put it: if you are not embarrassed about your first product, you launched too late.

First, clarify the interviewer's requirements and the goals, why do we need to build this, what problems are we trying to solve, who are our customers we are serving, why are you not happy with the existing solution?

Always start small, define a handful of critical product features first, and only launch it in one or two countries to test it out. And don't forget to mention you will always keep iterating and fine-tuning the algorithms/product features to expand its scope and bring it to more markets/countries.


Conclusion

I have shown you what a typical SQL interview (sometimes called technical data interview or data processing interview) process may look like. I also gave you some tips and techniques and a framework to answer that standard interview questions.

I hope you learned something today. If you have any questions or want some help with your job search, please feel free to reach out to me at instamentor.

Create your free SQLPad account and start practicing 90 SQL interview questions online.



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