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

Question

BlackTom AI · Accepted Answer

We’re asked which queries could return the same person–movie pair more than once, given constraints: at most one PRODUCED relationship and at most one REVIEWED relationship between any person and movie.

Option 1:
MATCH (p1:Person)-[:FOLLOWS]->(p2:Person),
      (p1)-[:REVIEWED]->(m:Movie)
RETURN p1.name, m.title;
This query forms a cartesian product between all pairs where p1 follows some p2 and where the same p1 has reviewed a movie m. If a given p1 follows multiple other people, and p1 has reviewed multiple different movies, you could produce multiple rows with the same (p1, m) pair for different p2s? Actually, for a fixed (p1, m) there could be repeated rows as a result of joining on multiple p2s that p1 follows. Therefore, the same (p1, m) could appear more than once. So this one can yield duplicates.

Option 2:
MATCH (p:Person)-[:REVIEWED]->(m:Movie)<-[:PRODUCED]-(p)
RETURN p.name, m.title;
Here, the same person p must both REVIEWED a movie m and be the PRODUCER of that same movie m to match. Given the constraint of at most one REVIEWED and at most one PRODUCED relation per person–movie pair, there is at most one path matching this exact pattern for any (p, m). Thus, this query cannot return the same (p, m) pair more than once due to duplication; it yields a single row per p–m if both relations exist.

Option 3:
MATCH (p:Person)-[:PRODUCED]->(m:Movie)
RETURN p.name, m.title;
This simply returns every produced relation. Since there is at most one PRODUCED relationship between any person and movie, you won’t get duplicates for the same (p, m) pair from multiple produced edges. Duplicates would require multiple identical PRODUCED edges, which the constraint forbids. So this one cannot produce repeats for the same pair.

Option 4:
MATCH (p:Person)-[r]->(m:Movie)
WHERE type(r) IN ['PRODUCED','REVIEWED']
RETURN p.name, m.title;
This query considers any single relationship of either type. A given (p, m) pair could have two different relationships simultaneously (one PRODUCED and one REVIEWED). In that case, there will be two rows for the same (p, m) pair: one for r being PRODUCED and one for r being REVIEWED. So duplicates are possible here.

Option 5:
MATCH (p:Person)-[r]->(m:Movie)
WHERE (p)-[:REVIEWED]->(m)
RETURN p.name, m.title;
This query returns a row for each relationship r from p to m, but only for those (p, m) pairs where p has REVIEWED that movie. If the same (p, m) pair also has a PRODUCED relationship (in addition to REVIEWED), there will be at least two matching rows: one for the r that is REVIEWED and one for the r that is PRODUCED. Therefore duplicates can occur when both relationships exist.

COMP4338 COMP5338 (NE) Out of Class Quiz -- Week 7

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

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