I built a free, interactive SQL practice tool for data engineering interviews

Harish Kumar Mula — Sat, 29 Aug 2026 06:51:15 +0000

Most data engineering interview prep resources I found online were static — a list of questions with answers underneath. You read the answer, nod, and move on. A week later you can't actually write the query yourself.

So I built a small free tool that flips that: you write the actual SQL, and it checks your logic instantly instead of just showing you an answer to read.

Live here: https://harish-dataengineer.github.io/de-interview-prep/

What's in it right now:

SQL questions covering things that actually come up in interviews — finding the second highest value, detecting duplicates, running totals with window functions, gaps in a login/activity sequence
Multiple-choice questions on core concepts: star vs. snowflake schema, ETL vs. ELT, idempotent pipelines, partitioning, slowly changing dimensions
Hints if you get stuck
No sign-up, nothing stored — it all runs in your browser

It's an early version — right now it's about 10 questions. I'm planning to add more (Python, dbt/Spark-specific questions, harder SQL) over the next few weeks based on what people actually find useful.

If you're prepping for data engineering interviews, or if you've been on the interviewing side and have questions you think should be included, I'd love feedback. Happy to take suggestions in the comments or as GitHub issues.

Repo: https://github.com/harish-dataengineer/de-interview-prep

DEV Community: Harish Kumar Mula

I built a free, interactive SQL practice tool for data engineering interviews