How to smash a SQL interview

I’ve interviewed for Data Science and Analytics roles at 20+ companies. 95% of them involved a SQL interview.

Yes, that’s a lot of SQL interviews.

If you’re interviewing for Data roles, you can pretty much expect to get a SQL interview.

Over the years, I failed a lot of SQL interviews. And later, I started crushing a lot of SQL interviews.

Throughout all of that, I refined my approach on how to tackle these interview questions. And now, I really believe I’ve figured out a foolproof way to nail them.

It comes down to having a formula for tackling these interviews. You don’t need to reinvent the wheel every time you face a SQL interview. You just need to follow a repeatable, reliable process.

So let’s get into it.

#1 Reframe the question and ask clarifying questions

Always start by confirming your understanding of the question. I do this by reframing the question in my own words. This shows my thought process and gives the interviewer a chance to correct me before I dive in. (Just in case I misunderstood or misinterpreted the question)

If the question involves some ambiguity, this is also your chance to clarify and align with your interviewer.

For example, if the interviewer asked you a question like: "What is the growth rate of X metric?"

There are so many ways to define growth:

→ Do we want absolute change or relative change?
→ Are we looking at long-term growth or short-term growth?

Use this first step as a chance to solidify how you will approach the question. This discussion shows off your product sense and great communication skills.

#2 State assumptions you have about the data

Typically, a SQL question would come with one or more tables. Before starting to write any queries, I find it helpful to state my assumptions on the table(s).

This step is so underrated, but it helps avoid misunderstandings and shows that you’re familiar with relational database concepts.

Some assumptions you can state include

• Which column is the primary key?

• Which columns are the foreign keys?

• Can an event take place multiple times?

• Are there any columns with unique values?

#3 Outline your approach

Again, you want to demonstrate your ability to communicate clearly and solve problems systematically.

I feel like a broken record saying the same thing over and over again. But the point I want to drive home is: you want to use your SQL interviews to demonstrate strong communication skills, and structured problem-solving approach.

There are a couple of good ways to outline your approach:

• Bullet points → Outline the key steps you'll take (join tables, filter, aggregate, etc.)

• Pseudocode → Quickly sketch out what the query will look like (especially useful if you’ll use multiple CTEs)

But if it’s a simple question, you don’t need to overdo it. Just talk through your approach out loud.

#4 Fill in your SQL query (talking aloud as you go)

Alright — now it’s time to actually write the query.

You’l be surprised how much easier this becomes because of all the steps you’ve completed before this. By now, you’ve already:

→ Clarified the question
→ Aligned on assumptions
→ Outlined your approach

At this point, your brain can go on auto-pilot as you fill in the blanks. As you code, talk through what you’re doing out loud, focusing on explaining your logic.

Side note, I personally also like doing this because it fills in the awkward silence.

#5 Review your query — catch any errors

In my opinion, this is the most important step.

I’ll say it again, this is the most important step.

Before you lock in your answer, take a minute to do a thorough review of your query.

Please… do not skip this step.

Why?

✅ Because if you catch the errors → that shows attention to detail.
❌ If your interviewer catches the errors → that shows a lack of skill.

Slow down here. It's worth it.

#6 Provide suggestions for improving the query

THIS is how you demonstrate that you’re a thought leader, and not a SQL monkey.

Finishing the query isn’t enough. That’s the baseline expectation.

You want to stand out from the crowd.

At the end of each query, answer at least one of these questions:

• What are edge cases that the query did not catch?

• What are some ways to optimize your query?

• What are some drawbacks to this approach?

Now go smash your next SQL interview. You got this.

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