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// case studies · real world impact
Solve free real-world SQL case studies from top companies — full schema, dataset, solution, and business insight. Great for interview prep.
// real world impact
Solve free real-world SQL case studies from top companies — full schema, dataset, solution, and business insight. Great for interview prep.
Browse Case Studies Interview questions// SELECT A CASE STUDY
Case Studies
Select a case study from the sidebar
Browse the list on the left and click any case study to open it.
Questions test whether your SQL runs. Cases test whether you can own a decision. Learn this once, use it everywhere below.
Restate the grain
One output row = one what? Write it down first — every GROUP BY and join must serve that grain.
Explore before you aggregate
Eyeball every table first: NULL join keys, orphan keys, date coverage. Ten minutes here saves an hour of debugging.
Hand-trace one entity end to end
Compute one row's answer by hand, then demand your query agree. Trust the trace, not the query.
Build incrementally, validate each CTE
Run each CTE standalone and reconcile counts before stacking the next one.
Pressure-test boundaries and empties
Probe cutoffs, zero-activity entities, ties, and empty results — interviewers live on boundaries.
Recommend, don't just report
End with a decision, an owner, and what would change your mind. No recommendation, no case study.
// FAQ
The starter case studies are completely free with no signup — full business problem, dataset, schema, and solution. Advanced studies are part of the paid challenge packs.
No account is needed to read every case study summary. A free account unlocks the interactive SQL console with instant feedback and saves your progress across devices.
Every study ships the real-world business problem, the dataset description, the full database schema with seed data, the reference SQL solution with a step-by-step explanation, and the business insight the analysis produced.
Interview questions are standalone problems for speed and accuracy drills. Case studies are end-to-end business scenarios — context, messy data, analysis, and insight — mirroring take-home assignments and analytics interviews. Do both: drill the question bank, then prove judgment on cases.
Yes — start with Beginner studies covering SELECT, JOINs, and aggregations, then progress to window functions and CTEs. If the SQL itself feels new, work through the Learn SQL Roadmap first and return here to apply it.
Studies span Retail, Fintech, SaaS, Healthcare, and more, each modeled on the analytics problems those businesses actually solve — revenue analysis, churn, fraud, funnel conversion, and operations.