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.
Transactions, Constraints, and Upserts / predict result
M32-A01 - Prediction: Transactions, Constraints, and Upserts
M32-A01 - Prediction: Transactions, Constraints, and Upserts. Protect multi-step changes with transactions and rely on constraints for integrity.
- Result grain
- one returned changed row
- Exact columns
- employee_id; active
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Cursor at line 1, column 1.
Scenario
Use the visible seed to understand the task, then pass hidden deterministic variants.
Transactions, Constraints, and Upserts / predict result
One-sentence task
M32-A01 - Prediction: Transactions, Constraints, and Upserts. Protect multi-step changes with transactions and rely on constraints for integrity.
Learn mode disclosure
Theory, concept names, full schema help, and progressive hints are available.
Structured output contract
- Result grain
- one returned changed row
- Exact columns
- employee_id; active
- 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
- single-dml; hidden deterministic variants.
Relevant tables
Time and difficulty
- Estimated time
- 7 minutes
- Difficulty
- 4/5
Objective and concepts
State the requested SQL output contract for transactions, constraints, and upserts 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
UPDATE <target_table>
SET <changed_column> = <safe_expression>
WHERE <narrow_key_or_population>
RETURNING <audit_columns>;- <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
The key predicate targets one row, and RETURNING makes the changed row inspectable.
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
UPDATE employees SET active = FALSE WHERE employee_id = 6 RETURNING employee_id, active;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.
- Affected rows
- Constrain mutation scope narrowly and return audit columns that prove which rows changed.
PostgreSQL-compatible local checks
Queries run in a local PGlite worker with PostgreSQL-style syntax and transactional grading.
- Wrong grain: The row count looks plausible but duplicates or missing zero rows appear. Repair: Name the intended grain, then inspect joins and GROUP BY clauses against that grain.
- Unstable order: The same rows appear in a different order during checks. Repair: Add a deterministic secondary sort key when ties are possible.
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