Stabilize retention cohort matrix

sqlMEDIUMSQL

Stabilize retention cohort matrix

Medium SQL arena: date bucketing, joins, and cohort aggregation

XP reward

185

Coins

Target time

27m

Mission locked

Missing prerequisites: sql-easy-retention-cohorts

Product wants week-one and week-four retention without double counting returning users. You are working inside an analytics warehouse, and the arena only clears when the result is safe, deterministic, and explainable.

Learning objective

Learn to apply date bucketing, joins, and cohort aggregation in an analytics warehouse while explaining the invariant, safety constraints, and hidden edge cases.

Mission order

users(id, created_at) and events(user_id, event_name, occurred_at). Handle normal data, malformed data, and deterministic ordering before optimizing. Submit the solution plus enough reasoning to pass hidden edge cases.

Visible checks

returns read-only result set

Expected: no mutation statements

uses deterministic ordering

Expected: stable review output

Clear requirements

Demonstrates date bucketing, joins, and cohort aggregation
Handles the visible sample and hidden edge cases
Keeps output deterministic and explainable
Stays read-only

Secure validation contract

Judge type

SQL

Complexity target

Planner-aware read-only query with deterministic output

SQL schema

users(id, created_at) and events(user_id, event_name, occurred_at).

Workspace

SQL query console

locked

Clear the route first

You can read the mission brief, but the editor, hints, tests, and submit flow stay locked until progression or plan access catches up.

Enter Immersive

Test Results

Run the visible checks when your first pass is ready.

Clear Protocol

1Read the scenario and restate the expected output shape.

2Run visible checks before chasing hidden edge cases.

3Use Genie for one nudge if stuck, then explain the invariant.

4Submit only when the result is deterministic and safe.

Rewards

185

Coins

Mission Route

Previous Next

Back to catalog

Hints

Hints are metered and logged for No Hint Hero runs.

Genie Mentor Core

Hint protocol / contextual guardrails active

Progressive hints

Failed-test aware

Solution guarded

Mission: sql-medium-retention-cohorts0 attempts0 failed tests0 hints used

Progressive hint depth

Genie: Genie online. I use your mission, attempts, failed tests, hints, and path context to coach the next rep without dumping answers first.

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sqlMEDIUMSQL