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SQL

SQL for Data Engineering

The SQL an interview loop actually asks for: grouping, windows, and the shapes that separate a screen from an offer.

11 questions across 3 modules, in the order the concepts build. Each one is graded by running it.
  1. 1
    Grouping and duplicates
    Rank within a group, and tell a duplicate from a repeat.
    SQLSQLFree0/3
  2. 2
    Windows and time
    Carry a value across rows: running totals, as-of joins, late data.
    SQLSQLLocked
    • Running balance per accountMedium
    • Rolling 7-day active usersMedium
    • Month-over-month revenue growthMedium
    • Latest price as of each orderMedium
    • Late arriving events per visitorMedium
  3. 3
    Sessions, cohorts and islands
    The three shapes that separate a screen from an offer.
    SQLSQLLocked
    • Sessionize clickstream eventsHard
    • Gaps and islands in device uptimeHard
    • Cohort retention by signup monthHard