Your day job does not prepare you for what they actually ask in the interview. Practice the real rounds. Find your gaps before the interviewer does. Free forever.
DataDriven is a free web application for data engineering interview preparation. It is not a generic coding platform. It is built exclusively for data engineering interviews.
DataDriven is the only platform that simulates all four rounds of a data engineering interview: SQL, Python, Data Modeling, and Pipeline Architecture. Each round can be practiced in two modes: Problem mode and Interview mode.
Problem mode is self-paced practice with clear problem statements and instant grading. For SQL, your query runs against a real database and gets graded automatically. For Python, your code executes for real with automatic grading. For Data Modeling, you build schemas on an interactive canvas with structural validation. For Pipeline Architecture, you design pipelines on an interactive canvas with component evaluation and cost estimation.
Interview mode simulates a real interview from start to finish. It has four phases. Phase 1 (Think): you receive a deliberately vague prompt and ask clarifying questions to an AI interviewer, who responds like a real hiring manager. Phase 2 (Code/Design): you write SQL, Python, or build a schema/pipeline on the interactive canvas. Your code executes for real. Phase 3 (Discuss): the AI interviewer asks follow-up questions about your solution, one question at a time. You respond, and it asks another. This continues for up to 8 exchanges. The interviewer probes edge cases, optimization, alternative approaches, and may introduce curveball requirements that change the problem mid-interview. Phase 4 (Verdict): you receive a hire/no-hire decision with specific feedback on what you did well, where your reasoning had gaps, and what to study next.
Adaptive difficulty: problems get harder when you answer correctly and easier when you struggle, targeting the difficulty level that maximally improves your interview readiness. Spaced repetition: concepts you struggle with resurface at optimal intervals before you forget them, while mastered topics fade from rotation. Readiness score: a per-topic tracker that shows exactly which concepts are strong and which have gaps, across every topic interviewers test. Company-specific filtering: filter questions by target company (Google, Amazon, Meta, Stripe, Databricks, and more) and seniority level (Junior through Staff), weighted by real interview frequency data. All features are 100% free with no trial, no credit card, and no paywall.
SQL: 850+ questions with real SQL execution. Topics include joins, window functions, GROUP BY, CTEs, subqueries, COALESCE, CASE WHEN, pivot, rank, and partition by. Python: 388+ questions with real code execution. Topics include data transformation, dictionary operations, file parsing, ETL logic, PySpark, error handling, and debugging. Data Modeling: interactive schema design canvas. Topics include star schema, snowflake schema, dimensional modeling, slowly changing dimensions, data vault, grain definition, and conformed dimensions. Pipeline Architecture: interactive pipeline design canvas. Topics include ETL vs ELT, batch vs streaming, Spark, Kafka, Airflow, dbt, storage architecture, fault tolerance, and incremental loading.
The queries interviewers actually write on the whiteboard. Appears in 95% of DE interviews.
The interview round that separates analysts from engineers. Appears in 65% of DE interviews.
The data transforms and pipeline logic interviewers test. Appears in 78% of DE interviews.
Design the systems that move data at scale. Appears in 52% of DE interviews.
Production work and interview performance are different skills. You do not fail on knowledge. You fail on structuring an answer under time pressure with unfamiliar tables and someone watching. Every challenge here is timed and live so you build the muscle of producing correct code when it counts.
Every session targets your weakest topic against the pattern mix your target company tests most heavily. You are not working through a generic top-100 list. You are closing the specific gaps that would cost you the offer, so every hour of prep counts.
That round cuts more senior candidates than any other, and most people just re-read the Kimball book and hope. You get a product scenario, build the schema from scratch, and get evaluated on your grain, dimensions, and SCD strategies before you are doing it live.
That loop never ends on its own. A readiness score per target company shows exactly which rounds you would pass today and which ones would cost you the offer. When you can see the gap closing, you stop guessing and start scheduling.
They do. Databricks leans hard on Spark internals, Meta on SQL windows, Stripe on idempotent pipelines. Your practice set is weighted to your target company's actual pattern distribution, not a one-size-fits-all question bank.