50N00 internal error in SlottedRewriter for FOREACH + COUNT {} + UNION ALL query #13720
Description
Configuration
Neo4j Version: neo4j:latest (pulled 2025-11-27)
Operating System: WSL2 – Ubuntu 24.04.1 LTS
Installation Method: Docker (neo4j:latest)
API/Driver: cypher-shell inside container
More Info:
neo4j@neo4j> CALL dbms.components() YIELD name, edition, versions
RETURN name, edition, versions;
+----------------------------------------------+
| name | edition | versions |
+----------------------------------------------+
| "Neo4j Kernel" | "community" | ["2025.10.1"] |
| "Cypher" | "" | ["5", "25"] |
+----------------------------------------------+
Steps to reproduce
- Start neo4j via Docker
docker run -d \
--name neo4j \
-p 7474:7474 -p 7687:7687 \
-e NEO4J_AUTH=neo4j/test12345 \
neo4j:latest
- Connect with cypher-shell
docker exec -it neo4j cypher-shell -u neo4j -p test12345
- Run the following query
MATCH (n)
DETACH DELETE n;
FOREACH (x IN [1] |
CREATE
k3 = (n)-[:R]->(:C {
agg: COUNT {
WITH DISTINCT *
MATCH () WHERE false
RETURN 1 AS v
UNION ALL
MATCH () WHERE false
RETURN 2 AS v
}
})-[:R]->(n)
);Expected behaviour
The query executes successfully, since all used features are documented as supported (FOREACH, COUNT subquery with UNION ALL, etc.).
Actual behaviour
The query fails with an internal processing error:
0 rows
ready to start consuming query after 2 ms, results consumed after another 0 ms
50N00: general processing exception - internal error. Internal exception raised SlottedRewriter$: Did not find `n` in the slot configuration of Projection (Id(17))
Key Points:
- The query fails with 50N00 internal error (SlottedRewriter$…), which indicates a server-side processing bug.
- If this combination is intentionally unsupported, I would at least expect a clear Neo.ClientError.* style message explaining the limitation, rather than an internal error.