Hands-on SQL Practice For A Data Science Interview

I bet you're searching the internet for a fantastic reference to help you get ready for your SQL interview. You've landed in the right place.

Let's jump right in and get started. I have a SQL browser available for you to use here: Show me the data

The data is fictitious, but extensive and useful for writing queries.

You can use this browser to answer all of the questions below. When you're done, if you weren't able to answer a couple of the questions, you can give me your email address in the email form near the bottom of this article and I'll send you the query solutions.

This article is designed to help you with "white boarding" SQL questions. We're not going to cover any theory here. Just a bunch of questions and how to answer them leveraging SQL.

I wish you a ton of luck on your interview, I hope it results in an offer! If you're looking to further your SQL skills for data science, I have also created the ultimate course in SQL for data science. We cover tons of material that you won't see here, because feature engineering, handling NULLs, working with datetimes, etc., is not typically part of the interview. But if you want to really hit the ground running at your new job, I'd highly suggest this course. It's free and you can find it here

SQL Questions using just the select statement:

• Write a query to determine the number of rows in the customer table. Answer: 351,962

• What was the maximum commission paid in the customer table? The median? Answer: Max -$10,295, Average -$66.30

• Write a query to that returns the customer_id, business_type and Country from the customer table.

SQL Questions using a where statement:

• How many customers do we have "has_instagram" information for in the customer table? i.e. - How many rows are not NULL? Answer: 128,449

• How many customers have a "First_conversion_date" greater than 1/1/2016 in the customer table? Answer: 54,397

SQL Question using a group by statement:

• How many customers have "has_facebook" =1 in the customer table? Use a group by statement. Answer: 60,894

SQL Question using a group by and order statement:

• Which state has the most customers? How many customers live in that state in the customer table? Answer: California, 43,736 customers

SQL Question using a having statement and subquery:

• Using the billedservices table, how many customers had more than 1 billed service? Use a subquery to answer this question. Answer: 44

SQL Question requiring a join:

• How many customers from OUTSIDE the United States have an entry in the billed services table? Answer: 89

In an interview, they'll typically place two or three pieces of paper up on the whiteboard. This will have your data. Obviously, this means that the data you'll be working with is much smaller.

Take home tests are typically much more difficult than what was covered here. During an in-person interview, they'll typically only have 30 minutes to an hour to assess your SQL knowledge. Most often, they just want to know that if you have SQL listed on your resume, that you can write some simple queries like up above.

I've never personally been asked to whiteboard the solution for creating a table, updating a column, etc., but obviously any SQL questions are fair game.

If you had no difficulty answering these questions, you're likely to do fine on your SQL interview.

Want to further your SQL skills for data science? Check out the Ultimate SQL for Data Science course.

Looking for the solutions to the questions above? I'll send them directly to your inbox :)