SQLPad FAQ 🙋‍♀️

Answers to some of the most asked questions.


Common general questions.

7 answers
Who is behind SQLPad?
Last updated at April 18, 2022

Leon Wei, SQLPad founder Hi, my name is Leon Wei. Most recently, I was a senior manager of machine learning at  Apple. You can read more about me at my mentor's page on instamentor.

I’ve been using SQL for over 10 years, and it is still my go-to programming language to prepare data.

Before that, I lead a team of data scientists and engineers at Chegg, helping students or young professionals to improve their performance at school or work.

I also worked as a research scientist at Amazon, focusing on building a large-scale real-time pricing optimization engine for their online retail business. 

The questions seem to be so easy, why?
Last updated at April 19, 2022

We created the cracking the SQL interview for the data scientist course with a beginner's mindset, and we assume our audience has 0 experience with SQL.

That's why the first 10 questions may seem to be very easy for experienced users, but you will find more and more challenging and tricky hard level questions as you move along to later questions.

Why choose SQLPad vs. Leetcode?
Last updated at April 18, 2022

SQLPad is the Leetcode alternative that makes learning and mastering SQL for data analytics professionals instead of software engineers. It creates a complete SQL mastery path for all data scientists.

🧑‍💻 Our approach to tackling a SQL interview is to first teach you SQL fundamentals with the cracking the SQL Interview for data scientists course before asking you to jump into the coding war.

📹 More than 20 video lectures to learn SQL fundamentals and tips and tricks help you understand what a SQL interview is about.

🏋️‍♀️ After you grasp the basics, you then jump into SQL coding questions that challenge you and make sure you mastered those SQL fundamental concepts.

😱 Leetcode jumps directly into some super long, hard-to-understand SQL coding questions that may frustrate you, especially if you just started.

📈 Instead, SQLPad has a more gradual, more user-friendly learning experience for all SQL skill levels.

🍿 The first 80 SQL coding questions are based on the same Movie rental database, which resembles a real-world commerce business.

🤗 From easy-level questions to challenging ones, you gradually build up a good understanding of the database schema by practicing those questions.

👩‍💻 And by the time you are to solve some of the most advanced SQL interview questions (#58-80), such as WINDOW functions and LAG/Lead, you are already familiar with those tables. You can jump right into the coding environment after learning the concepts.

Can I use your SQL problems and course materials somewhere else?
Last updated at April 18, 2022

Unfortunately NO.

I have designed and created the entire SQL course and curated all 180 SQL coding questions single-handedly, which took me 3000 hours of hard work, therefore you are not allowed to use any of those questions outside of this website, without my written permission.

If you represent a company and are interested to acquire a license to use my interview problems and solutions, please feel free to contact me.

What is SQLPad's goal?
Last updated at April 18, 2022

The goal of sqlpad is to help people in data analytics/science quickly learn or refresh their SQL skills.
It could be for a job interview or be more productive at work.

Why did you create sqlpad.io?
Last updated at April 18, 2022

After launching the Cracking the SQL Interview for Data Scientists course, I realized the need for my students to easily follow the course and practice SQL coding problems.

Since I can't find a solution online, I built SQLPad.

All the SQL exercises can be practiced in a browser, and my students don't have to waste hours configuring the database on their own computers.

I created both instamentor and sqlpad.

Who is SQLPad and the Cracking the SQL Interview course for?
Last updated at April 18, 2022

The Cracking SQL Interview course is a comprehensive course but is really focused on improving your SQL interview skills, with tips and techniques that I've learnt from interviewing thousands of data professional candidates. It saves time by concentrating on things that really matter.

We have seen satisfied customers ranging from fresh college STEM students searching their first industry jobs, and young professionals who want to switch their career track to work on data science.

SQLPad and the SQL interview course significantly improved their hands-on data processing capabilities, with laser-focused learning materials, to help land their dream job offers.


Common technical questions.

6 answers
Can you learn sql on a mac?
Last updated at Aug. 31, 2022

Yes, you totally can.

SQL interview questions and  SQL Playground work in all modern web browsers, including Chrome, Safari, Firefox in  Mac, Windows, Linux  and other operating systems.

Some of your solutions are not optimized, why?
Last updated at April 18, 2022

Good question, I created the solutions in a specific style/format (e.g., using IN instead of JOIN), so my students who take the Cracking the SQL interview for Data Scientists Course can follow along.

I have been gradually adding more solutions (optimized) and will indicate if that solution is for more advanced users.

If you have a better solution than mine, please feel free to let me know!


What is a SQL interview and why it is important?
Last updated at April 18, 2022

SQL is a must-know programming language for any analytics track data scientists, it is the lingua franca for processing and managing data in the industry. I’ve been using SQL for many years, and it is still my go-to language to prepare and manage data.

However, it is not a strong-typed language, and there are many popular database systems with different syntaxes and built-in functions, it could be very confusing for first-timers.

As a hiring manager or part of the hiring committee, I often ask a lot of SQL questions during a data scientist job interview, and to make sure the candidate will be hands-on at work.

However, in my 15 years career, I have met so many fresh college graduates or young professionals starting their job searches without solid coding skills in SQL, and in the end, they didn’t get a job offer.

The SQL interview can bear other names and may be called  Technical Analysis or Data Interview during a FAANG company interview, you might be asked to perform a series of SQL operations to extract data and insights, and answer follow-up questions about their products.

(*) FAANG: Facebook, amazon, apple, Netflix and google

What database engine is SQLPad based on?
Last updated at April 18, 2022

(Update 01/26, 2022, we now also support MySQL, more info.)

Great question, SQLPad's online playground, and the coding challenge's online judge is currently based on the latest Postgres.

Its query syntax is similar to other databases such as MySQL or Microsoft SQL Server, one of the major differences is on Postgres's DateTime related functions.

More details can be found here: https://www.postgresql.org/docs/current/functions-datetime.html

For example, there is no datediff function in Postgres, but you can subtract one DateTime column from another directly using the minus '-' operator, which is actually quite convenient and easier to type once you get the hang of it.

If you would like to see other database engines implemented on SQLPad, please let us know.



Do you support dark mode?
Last updated at April 18, 2022

sqlpad.io currently does not support dark mode, but we plan to add native support sometime this year.

In the meantime, we recommend you use a browser extension such as Super Dark Mode (if you use chrome), or similar Dark mode extensions for other browsers.

I just graduated, how should I get started looking for a job?
Last updated at April 18, 2022

There is definitely a lot to prepare for your first job hunt, especially given the current COVID-19 situation, hiring managers to receive a lot more applications from qualified candidates, and it pushes the hiring bar significantly higher than before.

If you are interested to know more about how to prepare a data scientist interview, I wrote a blog to explain different types of data scientists tracks.

And if you are interested in finding a job search mentor to help you get started with a concrete plan. Feel free to hire me.


Common account questions.

5 answers
I have found my dream job and would like to cancel my subscription, how can I do it?
Last updated at April 18, 2022

Absolutely, congratulations, and we totally understand you need to take a break and celebrate.

To cancel your subscription, simply:

1. Sign in to your account, go to your account dashboard, then click Manage Plan.

sqlpad | manage subscription

2. A customer portal page will pop up (Hosted on Stripe). Follow the step-by-step instructions to cancel your subscription.

What happens after?

You will still have access until the end of your subscription period, similar to Netflix.

If you want to delete your account permanently, shoot us a message with your username and email, and we will delete your account within 24 business hours.

My account has reached the free tier limit, what is that?
Last updated at May 24, 2022

You are given 10 FREE SQL coding questions to try out, after that, your account will be locked.

Upgrade to a paid plan will unlock it immediately and also give you access to all questions and solutions, as well as the cracking the SQL interview course (20 video lectures).

On average, it takes about 3-4 months to finish all the coding questions.

Can I expense the SQLPad subscrption from my employer?
Last updated at April 18, 2022

Absolutely, we have many customers who successfully get reimbursed their monthly subscriptions from their employers.

Most companies have a dedicated training/learning budget for their employees, and some companies auto approve for any expense less than $100.

Here is a sample invoice our customers have used to get reimbursed.

SQLPad sample receipt for reimbursement from employer


Do you offer one time order?
Last updated at Aug. 30, 2022

We currently don't offer one-time orders.

However, you can subscribe to the monthly service, pay for the first month and unsubscribe.

After your subscription expires, you won't be charged the next month, and all of your solutions will be persisted and ready to be accessed the next time you re-subscribe.

Is there a refund policy?
Last updated at April 18, 2022

Since we have already provided you a FREE tier to practice a limited set of questions, we cannot refund you once your subscription starts.

Cancellation and Refund Policy

1. Monthly/Quarterly subscriptions
Once your subscription starts, you CAN NOT get a refund for any payments you've already made.
If you don't want to subscribe anymore, cancel your subscription.

You will have access to the subscription until the end of the period you have paid for.

2.  One time purchase

Unfortunately, we can not refund one-time purchases, including but not limited to EBook, Ultimate Bundle, and Job Search ultimate bundle.

Have more questions? Please feel free to contact us, we read and respond to every email you send us, just give us some time. 😃