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AND, OR, NOT, and Parentheses / write query
M06-A05 - Negation - express a business exclusion without double-negation confusion
M06-A05 - Negation - express a business exclusion without double-negation confusion. Compose Boolean conditions and make mixed precedence explicit.
- Result grain
- one row per order not excluded by the business rule
- Exact columns
- order_id; status
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Cursor at line 1, column 1.
Scenario
Compose Boolean predicates deliberately: separate required conditions from alternatives, use NOT with explicit scope, and parenthesize mixed AND/OR logic.
AND, OR, NOT, and Parentheses / write query
One-sentence task
M06-A05 - Negation - express a business exclusion without double-negation confusion. Compose Boolean conditions and make mixed precedence explicit.
Learn mode disclosure
Theory, concept names, full schema help, and progressive hints are available.
Structured output contract
- Result grain
- one row per order not excluded by the business rule
- Exact columns
- order_id; status
- 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
- return order_id; exclude returned orders; exclude cancelled orders; order by order_id
- Validation
- select-only; hidden deterministic variants.
Relevant tables
Time and difficulty
- Estimated time
- 8 minutes
- Difficulty
- 2/5
Objective and concepts
Debug the requested SQL output contract for and, or, not, and parentheses 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
AND binds before OR, so parentheses are required when the shared condition must apply to both alternatives.
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, category, stock_count FROM products WHERE (category = 'Gear' OR stock_count = 0) AND NOT discontinued 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.
- SQL does not evaluate all predicates left to right: A mixed AND/OR filter returns rows from an alternative branch without the required condition. Repair: Remember AND binds before OR, then add parentheses around intended alternatives.
- OR is not a loose AND: A row is expected to satisfy both alternatives when the contract says either. Repair: Use OR for alternatives and AND for requirements that every row must meet.
- NOT needs an explicit scope: Only the nearest comparison is negated when the whole business phrase should be excluded. Repair: Put the excluded phrase in parentheses before applying NOT.
- Parentheses are semantic: Removing parentheses changes which rows survive hidden crossover cases. Repair: Treat parentheses as the source of truth for grouped alternatives.
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