Boss Battles

Capstone-style coding missions. Each Boss Battle combines several concepts you have practised separately into one substantial SQL or PySpark problem, written and graded in the same editor used for regular practice. The estimated time is a guide, not a timer.

The Retention Report

Build a per-user D1, D7 and D30 retention report that keeps every signup, including the users who never came back.

SQL · Advanced · about 35 minutes

Skills: Outer joins that keep every user, Per-user date arithmetic, Conditional aggregation into 1/0 flags, Assembling a combined result field

The Sales Leaderboard Rebuild

Rebuild a regional sales leaderboard from a feed with duplicated transactions and publish exactly the top two sellers in each region.

PySpark · Advanced · about 30 minutes

Skills: Deduplicating before aggregating, Grouped aggregation, Ranking within a partition, Top-N filtering per group

The Payroll Risk Monitor

Flag accounts whose latest salary credit fell more than 40% below their recent average, without false alarms from debits or thin history.

PySpark · Intermediate · about 45 minutes

Skills: Filtering to the relevant records, Window ranking per account, Aggregation with a history guard, Combining derived datasets, Threshold rules and rounding