What is a good SQL test for hiring?

A short test on a realistic two-to-four table schema with joins, a window function and a NULL or duplicate trap, plus one question where the candidate explains their result. Discuss it live.

What should a data engineer assessment include?

SQL, a Python task with an edge case, and a scenario on reliability or cost: for example a pipeline that finished green but produced wrong numbers.

What is pre-employment testing for data roles?

Testing a candidate's skills before an offer, usually a coding test (SQL, Python) and a scenario-based test or interview on real data judgement.

How long should a data skills test be?

Under two hours in total. Longer unpaid tests put off experienced candidates.

Can candidates cheat on online SQL tests with AI?

They can try, which is why you discuss the result live and add scenario questions where the reasoning matters more than the syntax.

Does carbon.talent have SQL and Python tests?

Yes, on paid plans. The real-world data experience test, which is scenario-based and not a coding test, is on every plan.

Guides · carbon.talent

SQL and Python skills tests for hiring

Last updated 18 Oct 2026

A good pre-employment data test checks the work the person will actually do: SQL for almost every data role, Python for engineers and scientists, and judgement on real data problems (broken pipelines, messy definitions, stakeholder pushback) for anyone senior. Use a short coding test to confirm the basics, a scenario-based test or interview for judgement, and keep the whole thing under a couple of hours. On carbon.talent the real-world data experience test is on every plan, and SQL and Python skills tests are on paid plans.

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Which test for which role

Role	SQL test	Python test	Scenario / judgement	Take-home?
Data analyst	Yes: joins, window functions, aggregation, NULLs	Optional	Yes: messy question, ambiguous metric	Short case, discussed live
Analytics engineer / dbt	Yes: modelling, incremental logic	Rarely	Yes: definitions, testing, change impact	Fix a small broken model
Data engineer	Yes	Yes: data handling, APIs, testing	Yes: incidents, cost, reliability	Optional, under two hours
Data scientist	Yes	Yes: pandas, modelling basics	Yes: framing, experiments, leakage	Short practical with a planted problem
ML / MLOps engineer	Light	Yes	Yes: deployment, drift, evaluation	System design discussion

Coding test vs scenario test

A coding test (SQL or Python, auto-scored) answers "can they write correct queries and code?" It's fast and consistent, and easy to over-weight: passing it says little about judgement on a messy real system.
A scenario test answers "what would they do when the dashboard is wrong at 9am?" It's what separates mid from senior.
Use both for most data roles: coding to confirm the floor, scenarios to find the strong ones.

What makes a fair data test

Looks like the job: your kind of data, your kind of question.
Short: under two hours in total. Long unpaid take-homes lose the best candidates.
Same for every candidate, scored on a written rubric.
Discussed live, so you see reasoning and can spot copied or AI-written work.
Allows normal tools (documentation, search) unless the point is recall.

What a good SQL test includes

A small schema of two to four tables that look like your business.
A join with a trap (duplicates or missing keys).
A window function (second order, running total, month-on-month change).
A NULL or data-type issue to handle.
One "explain your result" question. For analysts, add a vague business question and ask for a one-paragraph recommendation.

What a good Python test includes (engineers and scientists)

Read and clean a realistic file or API response.
A transformation with an edge case (time zones, late records, duplicates).
A simple test they write themselves.
For scientists: a quick model or analysis with one planted problem (leakage or a biased sample).

Testing on carbon.talent

Real-world data experience test (every plan): scenario-based questions on real data judgement for data engineering, analytics and DS/ML roles. It is not a coding test.
SQL and Python skills tests (paid plans).
Working-style profile and short video intro to complete a vetted profile. ID checks on Team and Scale.
Applicants' results show on their profile; or test a candidate you found by sending them the test yourself.

Tool landscape (for context)

Dedicated assessment vendors sell coding tests for all software roles; their SQL tests are a good fit if you only need auto-scored queries. carbon.talent is built for data roles and pairs the test with the hire itself (post, review, interview, contract). (Named-vendor comparison held back: see notes.)

Questions companies ask

What is a good SQL test for hiring?: A short test on a realistic two-to-four table schema with joins, a window function and a NULL or duplicate trap, plus one question where the candidate explains their result. Discuss it live.
What should a data engineer assessment include?: SQL, a Python task with an edge case, and a scenario on reliability or cost: for example a pipeline that finished green but produced wrong numbers.
What is pre-employment testing for data roles?: Testing a candidate's skills before an offer, usually a coding test (SQL, Python) and a scenario-based test or interview on real data judgement.
How long should a data skills test be?: Under two hours in total. Longer unpaid tests put off experienced candidates.
Can candidates cheat on online SQL tests with AI?: They can try, which is why you discuss the result live and add scenario questions where the reasoning matters more than the syntax.
Does carbon.talent have SQL and Python tests?: Yes, on paid plans. The real-world data experience test, which is scenario-based and not a coding test, is on every plan.