Harden duplicate transaction detector

sqlHARDSQL

Harden duplicate transaction detector

Hard SQL arena: GROUP BY, HAVING, tie-safe ordering, and read-only analysis

XP reward

340

Coins

Target time

40m

Mission locked

Missing prerequisites: sql-easy-duplicate-transactions

Payment retries created duplicate checkout events and finance needs a reproducible list. 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 GROUP BY, HAVING, tie-safe ordering, and read-only analysis in an analytics warehouse while explaining the invariant, safety constraints, and hidden edge cases.

Mission order

transactions(id, user_id, order_id, status, amount_cents, created_at). Design for correctness under duplicates, missing values, and high-volume input. 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 GROUP BY, HAVING, tie-safe ordering, and read-only analysis
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

transactions(id, user_id, order_id, status, amount_cents, created_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

340

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-hard-duplicate-transactions0 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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sqlHARDSQL