Mode disclosure
All modes use one coherent workspace; only disclosure and guidance change. Learn mode keeps theory, concept names, full schema help, progressive hints, and solution review available.
Workspace Orientation and First Run / predict result
DIA-01 - select two requested columns in exact order
DIA-01 - select two requested columns in exact order. Use the product without interface uncertainty; run, edit, check, and recover a first query.
- Result grain
- one row per product
- Exact columns
- product_id; product_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.
Scenario
Use the visible seed to understand the task, then pass hidden deterministic variants.
Workspace Orientation and First Run / predict result
One-sentence task
DIA-01 - select two requested columns in exact order. Use the product without interface uncertainty; run, edit, check, and recover a first query.
Learn mode disclosure
Theory, concept names, full schema help, and progressive hints are available.
Structured output contract
- Result grain
- one row per product
- Exact columns
- product_id; product_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 product_id ascending
- Validation
- select-only; hidden deterministic variants.
Relevant tables
Time and difficulty
- Estimated time
- 4 minutes
- Difficulty
- 1/5
Objective and concepts
State the requested SQL output contract for workspace orientation and first run using source grain, columns, ordering, and edge-case evidence.
Glossary links
Concept material
SQL Trail treats every query as an evidence trail: identify source grain, transform rows deliberately, then compare output to a shared contract.
A passing query must handle hidden nulls, ties, boundaries, and no-match rows when the contract makes them relevant.
Syntax card
SELECT <requested_columns>
FROM <source_table>
WHERE <source_population_filter>
GROUP BY <result_grain_columns>
ORDER BY <deterministic_tie_breakers>;- <requested_columns> means the exact output columns, aliases, and order from the visible contract.
- <source_population_filter> means the row population definition, not a copied visible-row value.
- <deterministic_tie_breakers> means all ordering and tie rules needed for repeatable output.
Why this works
Run executes the supplied query locally and shows status, row count, and result columns without marking the activity complete.
Edge cases
Hidden variants preserve nulls, ties, duplicates, boundaries, no-match rows, and alternate row order when those risks apply.
PostgreSQL note
The local engine uses PostgreSQL-compatible syntax, including explicit NULL predicates, deterministic ORDER BY clauses, and transactional grading.
Worked example
SELECT product_id, product_name FROM products ORDER BY product_id;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.
PostgreSQL-compatible local checks
Queries run in a local PGlite worker with PostgreSQL-style syntax and transactional grading.
- Run is not completion: The result grid appears, but the activity still needs a Check result. Repair: Use Run to explore visible rows, then use Check when the answer should be graded against visible and hidden variants.
- Visible rows are not the whole database: A copied visible result passes Run but fails when hidden variants add or change rows. Repair: Write the query rule, not the displayed rows, and let hidden variants test the rule.
- Schema panel is not the result: Column names in the schema are mistaken for rows returned by the query. Repair: Use the schema panel to choose tables and columns, then use Run to inspect actual result rows.
- Syntax errors do not destroy drafts: After an error, the learner expects their SQL to be erased or the attempt to be unrecoverable. Repair: Keep the draft, fix the highlighted SQL, and rerun locally before using Check again.
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