SQL and ETL mock interviews with an AI interviewer
In a SQL/ETL round, you write queries against a described schema (joins, aggregations, window functions), then talk through how you'd load, transform and validate the data reliably every day. Small mistakes, like a join that duplicates rows or a job that can't be re-run, are exactly what interviewers look for.
In PrepLinx you write and run SQL in the editor while an AI interviewer reviews your query and its output, asks how it performs on large tables, and pushes on the pipeline design around it.
What this round tests
SQL writing
Correct queries with joins, aggregations and window functions.
Query optimization
Indexes, partitioning, and rewriting slow queries.
ETL design
Extraction, transformation and loading that's reliable and safe to re-run.
Transformation logic
Getting the business rules right in the data.
Error handling
What happens when a load fails partway through.
Data quality
Validating data before anyone downstream uses it.
Practice questions
Examples of the questions and follow-ups you can expect. Practice saying your answers out loud, not just reading them.
- Find each user's first purchase and the number of days until their second.
- Return the top three products by revenue in each category.
- This query scans the whole table. How would you speed it up?
- How would you make a daily load safe to re-run?
- Design an incremental load from a source table that has updates and deletes.
- What checks would run before you publish a table to analysts?
How a PrepLinx session works
- 1
Choose the round
Pick the role, the interview type and a difficulty (easy, medium or hard). Optionally add a job profile with your resume and the job description, so the questions relate to that job.
- 2
Interview out loud
The AI interviewer speaks, listens to your answers and asks follow-ups. It doesn't give hints or say whether you're right, just like the real thing. The session runs up to 30 minutes.
- 3
Get scored feedback
A report with a 0–10 score for each dimension the round is graded on, strengths quoted from your own words, weaknesses, concrete improvements and an overall hiring signal, plus the full transcript.
How to prepare
Clarify the grain and keys
Ask what one row means and which columns are unique before you join anything.
Watch for join fan-out
Check whether a join can multiply rows, and say how you'd verify it doesn't.
Practice window functions
Get comfortable with ROW_NUMBER, RANK, LAG and running sums until you can write them without looking anything up.
Design for idempotency
Explain how your load behaves when it runs twice or fails halfway.
Mention data quality early
Row counts, null checks and freshness alerts show production experience.
Frequently asked questions
Can I run SQL during the interview?
Yes. Choose SQL in the editor and run your queries during the session. The interviewer sees your query and the result.
Which SQL dialect is used?
Queries run on SQLite, which supports joins, CTEs and window functions. Interviews care about the logic far more than dialect details, and you can mention how you'd write something in your warehouse's dialect.
Is this only for data engineers?
It's part of the data engineer track, but analysts, analytics engineers and data scientists with a SQL screen can practice it too.
How long is a session?
Up to 30 minutes.
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Practice your next SQL and ETL interview
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