Q 21: Which query returns total hours worked on each project?

Question

BlackTom AI · Accepted Answer

Aggregating the r.hours property grouped by each project requires matching Person→WORKS_ON→Project relationships and summing the hours on those relationships.

1) Relevant knowledge points and concepts
- Cypher pattern matching: MATCH (:Person)-[r:WORKS_ON]->(p:Project) finds WORKS_ON relationships r from Person nodes to Project nodes p.
- Relationship properties: r.hours is a property on the WORKS_ON relationship that records hours worked.
- Aggregation and implicit grouping in Cypher: When you RETURN a non-aggregated expression (p.code) together with an aggregate (SUM(r.hours)), Cypher implicitly groups results by the non-aggregated expression (p.code), producing one row per project code with the aggregate value.

2) Step-by-step reasoning
- Step 1: MATCH (:Person)-[r:WORKS_ON]->(p:Project) produces rows for every person who works on a project, each row containing the relationship r and the project node p.
- Step 2: For each matched row, read r.hours (hours that specific person worked on that project).
- Step 3: RETURN p.code, SUM(r.hours) tells Cypher to group rows by p.code and compute the sum of r.hours within each group.

3) Intermediate/calculation steps (conceptual)
- Suppose Project A has relationships with hours 5, 3, and 2. The matching step yields rows with r.hours = 5, 3, 2. SUM(r.hours) across rows for p.code = 'A' gives 5 + 3 + 2 = 10.
- This is performed for each distinct p.code.

4) Why the correct answer is correct
- It matches the correct pattern (Person → WORKS_ON → Project), accesses the hours stored on the relationship (r.hours), and uses SUM to aggregate those hours per project code (implicit grouping by p.code). That exactly yields total hours worked on each project.

5) Why other options are incorrect
- Option 2 (MATCH (p:Project) RETURN p.code, COUNT(*)): only matches Project nodes, not WORKS_ON relationships; COUNT(*) would count rows (projects), not sum hours.
- Option 3 (MATCH (r:WORKS_ON) RETURN SUM(r.hours)): incorrect syntax—(r:WORKS_ON) treats WORKS_ON as a node label; also it would (if relationships matched correctly) return only a single total across all projects rather than per project.
- Option 4 (MATCH (p)-[:WORKS_ON]->(r) RETURN SUM(p.hours)): flips node/relationship roles and sums a node property p.hours that likely doesn't exist—hours are on the relationship, not the node.
- Option 5 (None of the above): incorrect because the first option already does what's required.

6) Conclusion
The correct query is MATCH (:Person)-[r:WORKS_ON]->(p:Project) RETURN p.code, SUM(r.hours), which matches the provided answer.

Q 21: Which query returns total hours worked on each project?单项选择题

类似问题

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

Q25: Which query returns people who authored work from projects funded by Innovation?

Q 22: Which query returns works authored by someone who is also a Researcher?

Q 19: Which query returns the department that funds the project Alice works on?

Q 12: Which query returns only people who are BOTH Engineer AND Researcher?

Which of the following queries could return the same person–movie pair more than once, even if the dataset guarantees that there is at most one PRODUCED relationship and at most one REVIEWED relationship between any person and movie

Which queries find people who both acted in and directed the same movie in neo4j's sample Movie Graph? Select all that apply.

What is the effect on the financial statements when a company fails to adjust the unearned revenue account for revenues earned at year-end?

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单