Mode disclosure
All modes use one coherent workspace; only disclosure and guidance change. Practice mode uses a concise prompt, normal schema, optional hints, and the same local Run and Check pipeline.
Aggregate Functions and Null Semantics / predict result
M13-A01 - Prediction - compare COUNT star and COUNT nullable column on a tiny set
M13-A01 - Prediction - compare COUNT star and COUNT nullable column on a tiny set. Summarize filtered input with COUNT, SUM, AVG, MIN, and MAX correctly.
- Result grain
- one aggregate row comparing all rows with known nullable values
- Exact columns
- customer_rows; known_loyalty_tier_rows
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.
Scenario
Summarize complete filtered inputs with aggregate functions: preserve one-row report grain, distinguish COUNT star from COUNT expression, and keep empty SUM policy explicit.
Aggregate Functions and Null Semantics / predict result
One-sentence task
M13-A01 - Prediction - compare COUNT star and COUNT nullable column on a tiny set. Summarize filtered input with COUNT, SUM, AVG, MIN, and MAX correctly.
Practice mode disclosure
Concise prompt, normal schema help, optional hints, and the same checker workspace are available.
Structured output contract
- Result grain
- one aggregate row comparing all rows with known nullable values
- Exact columns
- customer_rows; known_loyalty_tier_rows
- Source population
- Use the prompt setup plus FROM, JOIN, WHERE, and subquery predicates as the source population. Visible rows are only examples.
- Grouping
- Group only at the requested output grain: one aggregate row comparing all rows with known nullable values.
- Ordering
- No display order requirement unless Check reports one.
- Validation
- select-only; hidden deterministic variants.
Relevant tables
Time and difficulty
- Estimated time
- 5 minutes
- Difficulty
- 3/5
Objective and concepts
Practice mode keeps the prompt concise; open hints only if you choose guided help.
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
- 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
No hints opened yet.