Mode disclosure
All modes use one coherent workspace; only disclosure and guidance change. Challenge mode uses minimal framing, reduced completion help, no hints during active assessment, and an optional timer.
Timer is optional, pausable, can be disabled, and never affects mastery.
Fan-Out, Pre-Aggregation, Self Joins, and Non-Equi Joins / state change
CH-H11 - rolling period metric with missing months and zero prior values
CH-H11 - rolling period metric with missing months and zero prior values. Detect independent one-to-many fan-out and pre-aggregate to a common grain.
- Result grain
- one plan output for the lookup
- Exact columns
- QUERY PLAN
SQL editor shortcuts: Ctrl or Command Enter runs the query, Ctrl or Command Shift Enter checks it, Alt H opens the next hint, Ctrl or Command slash toggles a line comment, Ctrl or Command Shift F formats the SQL, and Escape closes transient UI.
Cursor at line 1, column 1.
Challenge mode / technique labels hidden during active assessment
One-sentence task
CH-H11 - rolling period metric with missing months and zero prior values. Detect independent one-to-many fan-out and pre-aggregate to a common grain.
Challenge mode disclosure
Minimal challenge framing with technique labels hidden during active assessment.
Structured output contract
- Result grain
- one plan output for the lookup
- Exact columns
- QUERY PLAN
- Source population
- Use the prompt setup plus FROM, JOIN, WHERE, and subquery predicates as the source population. Visible rows are only examples.
- Grouping
- Do not collapse rows unless the contract explicitly asks for aggregation, distinct tuples, or set semantics.
- Ordering
- No display order requirement unless Check reports one.
- Validation
- select-or-explain; hidden deterministic variants.
Relevant tables
Time and difficulty
- Estimated time
- 14 minutes
- Difficulty
- 5/5
Objective and concepts
Minimal challenge framing keeps completion help reduced until debrief.
Assumptions, dialect notes, and common traps
- Duplicate policy
- Preserve duplicate facts unless the prompt explicitly asks for distinct tuples or set semantics.
- Null policy
- Preserve NULL, empty string, zero, and false as distinct values unless the contract says to display a fallback.
- Tie-breakers
- No display order is graded unless the contract names one; avoid treating physical row order as evidence.
- Zero-related entities
- Do not invent zero rows unless the contract asks for preserved parents, missing entities, or complete periods.
- Numeric tolerance
- Use exact semantic comparison unless the activity explicitly declares a numeric tolerance.
Opened hints
Hints are disabled during active review or challenge assessment and become available after submission or outside assessment mode.