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 / explain plan
CH-H12 - correctness-preserving query-quality and plan audit
CH-H12 - correctness-preserving query-quality and plan audit. Detect independent one-to-many fan-out and pre-aggregate to a common grain.
- Result grain
- one row per employee
- Exact columns
- employee_id; employee_name; manager_name
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-H12 - correctness-preserving query-quality and plan audit. 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 row per employee
- Exact columns
- employee_id; employee_name; manager_name
- 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
- order by employee_id
- Validation
- select-only; 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
- Use every ordering rule in the contract and end tied business metrics with deterministic secondary keys when needed.
- Zero-related entities
- Preserve requested zero-related, no-match, or complete-period entities and make display fallback explicit.
- 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.