Q26: Which query ensures each project appears only once, even if multiple people work on it?

Question

BlackTom AI · Accepted Answer

RETURN DISTINCT is the core mechanism that removes duplicate rows in Cypher, so returning DISTINCT p will collapse multiple matches of the same project node into a single result.

Relevant concepts:
- MATCH (:Person)-[:WORKS_ON]->(p:Project) finds every pattern where a Person works on a Project; if multiple people work on the same project, that project node p will be matched multiple times.
- RETURN p without DISTINCT yields one row per match, so duplicates can appear.
- RETURN DISTINCT p deduplicates identical p values so each project node appears only once.
- MATCH (p:Project) RETURN p directly enumerates all Project nodes once (Cypher returns each matched node a single time when matching by node variable), so it also yields each project just once.

Step-by-step reasoning with a simple example:
1. Suppose Project P1 has Person A and Person B linked: two pattern matches for p = P1.
2. Query A: MATCH (:Person)-[:WORKS_ON]->(p:Project) RETURN p
   - Matches produce two rows: p = P1, p = P1 → duplicates remain.
3. Query B: MATCH (:Person)-[:WORKS_ON]->(p:Project) RETURN DISTINCT p
   - Matches produce two candidate rows but DISTINCT collapses them to one row: p = P1.
4. Query C: MATCH (p:Project) RETURN p
   - Directly matches each project node once, so p = P1 appears a single time.

Why the correct answer is correct:
- Both B and C ensure each project appears only once. B deduplicates projects even when matched multiple times via relationships. C lists projects directly and returns each node once.

Why other options are incorrect:
- Option A returns duplicates when multiple people work on the same project.
- Option E (None of the above) is false because B and C do meet the requirement.

Final confirmation: The correct answer is "Both B and C," matching the provided answer.

Q26: Which query ensures each project appears only once, even if multiple people work on it?单项选择题

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