ArcadeDB may return `null` for a `COUNT { ... }` pattern subquery instead of the expected integer count. (original) (raw)

ArcadeDB version

Verified on:

arcadedata/arcadedb:latest
arcadedata/arcadedb:26.4.1-SNAPSHOT

Observed through the same request shape used by ArcadeDB Studio:

language: opencypher
serializer: studio

Environment

Docker on Windows host
ArcadeDB queried through the HTTP API: /api/v1/command/arcade
Request mode aligned with ArcadeDB Studio
Neo4j used as the Cypher reference engine for comparison

Describe the bug

ArcadeDB may return null for a COUNT { ... } pattern subquery instead of the expected integer count.

In the repro below:

Alice owns one Labrador
Bob owns one non-Labrador dog
Charlie owns one non-Labrador dog

Neo4j returns 1, 0, 0 for labCount.
ArcadeDB returns null for all three rows.

To Reproduce

Setup

CREATE (:Person {name: 'Alice', age: 30}), (:Person {name: 'Bob', age: 25}), (:Person {name: 'Charlie', age: 35}), (:Dog {name: 'Rex', breed: 'Labrador'}), (:Dog {name: 'Fido', breed: 'Poodle'}), (:Dog {name: 'Spot', breed: 'Dalmatian'});

MATCH (p:Person {name: 'Alice'}), (d:Dog {name: 'Rex'}) CREATE (p)-[:HAS_DOG]->(d);

MATCH (p:Person {name: 'Bob'}), (d:Dog {name: 'Fido'}) CREATE (p)-[:HAS_DOG]->(d);

MATCH (p:Person {name: 'Charlie'}), (d:Dog {name: 'Spot'}) CREATE (p)-[:HAS_DOG]->(d);

Query

MATCH (person:Person) RETURN person.name AS name, COUNT { (person)-[:HAS_DOG]->(dog:Dog) WHERE dog.breed = 'Labrador' } AS labCount ORDER BY labCount DESC;

Expected behavior

The result should be:

Alice, 1
Bob, 0
Charlie, 0

Actual behavior

ArcadeDB returns:

Alice, null
Bob, null
Charlie, null

Control cases

Control 1, the plain match without COUNT { ... } behaves correctly:

MATCH (person:Person)-[:HAS_DOG]->(dog:Dog) RETURN person.name AS name, dog.breed AS breed ORDER BY name;

Observed result:

Alice, Labrador
Bob, Poodle
Charlie, Dalmatian

Control 2, counting all dogs with ordinary aggregation also behaves correctly:

MATCH (person:Person) OPTIONAL MATCH (person)-[:HAS_DOG]->(dog:Dog) RETURN person.name AS name, COUNT(dog) AS dogCount ORDER BY name;