Node label disjunction patterns may match no rows

[Silence6666668]

ArcadeDB version
Observed on Docker images:

• arcadedata/arcadedb:26.4.2

Environment

• Host OS: Windows 10
• Architecture: x86_64
• Deployment: Docker
• ArcadeDB endpoint: HTTP /api/v1/command/arcade
• Request mode matches ArcadeDB Studio:
  • language: opencypher
  • serializer: studio
• Differential comparison target: Neo4j Community 2026.04.0

Describe the bug
ArcadeDB may match no rows for a node pattern that uses a label disjunction such as (n:A|B), even when nodes with both labels clearly exist.

In the minimized repro below, the graph contains one A node and one B node.
Neo4j returns both rows.
ArcadeDB returns no rows.

This does not look like a general label-matching problem, because the same nodes are matched correctly when each label is queried separately.

To Reproduce

Setup:

CREATE (:A {id: 1}),
       (:B {id: 2}),
       (:C {id: 3});

Query:

MATCH (n:A|B)
RETURN n.id AS id
ORDER BY id;

Expected behavior
Observed Neo4j result:

1
2

ArcadeDB should return the same two rows.

Actual behavior
Observed ArcadeDB 26.4.2 result:

0 rows

So the label-disjunction pattern behaves as if no matching nodes exist.

Control cases

Single-label matches work correctly on both engines:

MATCH (n:A) RETURN count(*) AS cnt;
MATCH (n:B) RETURN count(*) AS cnt;
MATCH (n:C) RETURN count(*) AS cnt;

Observed result on Neo4j and ArcadeDB 26.4.2:

cnt = 1

So the data and ordinary label lookup are fine.

The failure is specific to disjunction. Two-label and three-label forms both fail on ArcadeDB:

MATCH (n:A|B) RETURN count(*) AS cnt;
MATCH (n:A|C) RETURN count(*) AS cnt;
MATCH (n:B|C) RETURN count(*) AS cnt;
MATCH (n:A|B|C) RETURN count(*) AS cnt;

Observed results:

• Neo4j:
  • A|B: 2
  • A|C: 2
  • B|C: 2
  • A|B|C: 3
• ArcadeDB 26.4.2:
  • all four queries return 0

This makes the boundary much clearer:

• single-label node pattern: correct
• label-disjunction node pattern: no rows