Why These 50?
Hand-curated for maximum interview ROI.
A Curriculum, Not a Catalog
Five stages of ten problems, each building on the last. You never wonder what to do next — Stage 1 to Stage 5 takes you from SELECT to multi-CTE business scorecards. No random pattern-jumping.
Industry-Grade Multi-Table Schemas
Every problem runs on 8–15 table production schemas modeled on real businesses — retail, social, fintech, healthcare. The same shape of query you’d actually write at a Stripe, Airbnb, or Uber.
Both SQLite and PostgreSQL
Toggle dialects with a single click on any problem. Learn the cross-dialect differences as you go, so you’re never blindsided when you switch from one company’s stack to another.
Skill Coverage
How the 50 problems distribute across SQL topics.
FAQ
The first 10 problems (Stage 1) are completely free.
Stages 2-5 require a Premium subscription, which gives you access to all 1,625 problems across 15 production-grade datasets.
Ready to Master SQL?
Start with Stage 1 — graded instantly in your browser.
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