Code School of Analytics

SQL Practice

Real-life business problems on real tables. Read the scenario, write the query, and get it checked instantly.

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All topicsSELECT & FilteringSorting & LimitsAggregationJoinsString & Date FunctionsWindow FunctionsSubqueriesNULL & CASECTEs & RecursionSet OperatorsAnalytics Patterns
All levelsBasicIntermediateExpert
Intermediate25 pts

Ageing report for overdue invoices

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Intermediate25 pts

Build the 2025-26 league table from raw results

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Expert50 pts

Heartbeat shoppers: gaps between orders

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Expert50 pts

30-day retention by first-order cohort

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Expert50 pts

The net new MRR waterfall

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Expert50 pts

Does week-one API usage predict churn?

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Expert50 pts

Hot streaks: each club's longest run of wins

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Expert50 pts

Patients whose labs stayed abnormal on back-to-back tests

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Expert50 pts

What does surge pricing really do?

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Expert50 pts

How much of the fleet really flies each month?

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Expert50 pts

Longest listening streak (gaps and islands)

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Expert50 pts

Month-1 and month-2 retention by sign-up cohort

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