Silence6666668 opened a new issue, #2383:
URL: https://github.com/apache/age/issues/2383
**Describe the bug**
`UNWIND [null]` may produce a row whose value prints as `null`, but
`count(x)` still counts it as `1`.
In Cypher, `count(expr)` should count only non-null values. After `UNWIND
[null] AS x`, the single row has `x = null`, so `count(x)` should be `0`.
Instead, Apache AGE returns `1`.
**How are you accessing AGE (Command line, driver, etc.)?**
- PostgreSQL `cypher(...)` wrapper through the local Python
differential-testing harness
- Reproducible directly in `psql` inside the Docker container
**What data setup do we need to do?**
No graph data is required beyond creating an empty graph:
```pgsql
SELECT create_graph('fuzz_graph');
```
**What is the necessary configuration info needed?**
- Plain Apache AGE Docker image was enough
- Docker image in local repro: `apache/age`
- AGE extension version: `1.7.0`
- PostgreSQL version: `18.1`
- Graph name used in repro: `fuzz_graph`
- No extra extensions or special configuration were required
**What is the command that caused the error?**
```pgsql
SELECT * FROM cypher('fuzz_graph', $$
UNWIND [null] AS x
RETURN count(x) AS c
$$) AS (c agtype);
```
Returned result on AGE:
```text
c
---
1
```
**Expected behavior**
The result should be:
```text
c
---
0
```
Neo4j returns `0` for the equivalent Cypher query:
```cypher
UNWIND [null] AS x
RETURN count(x) AS c
```
**Environment (please complete the following information):**
- Version: Apache AGE `1.7.0`
- PostgreSQL: `18.1`
- Host OS: Windows
- Architecture: x86_64
- Deployment: Docker
**Additional context**
This appears to be a counting/null-semantics issue specifically around
`UNWIND`, not a general `count(null)` problem.
Direct control cases on the same AGE instance:
1. Plain `count(null)` behaves correctly:
```pgsql
SELECT * FROM cypher('fuzz_graph', $$
RETURN count(null) AS c
$$) AS (c agtype);
```
Observed result:
```text
0
```
2. `WITH null AS x RETURN count(x)` also behaves correctly:
```pgsql
SELECT * FROM cypher('fuzz_graph', $$
WITH null AS x
RETURN count(x) AS c
$$) AS (c agtype);
```
Observed result:
```text
0
```
3. `UNWIND [null] AS x RETURN x` shows that the produced row is indeed
`null`:
```pgsql
SELECT * FROM cypher('fuzz_graph', $$
UNWIND [null] AS x
RETURN x
$$) AS (x agtype);
```
Observed result:
```text
null
```
A larger differential-testing case first exposed this via:
```cypher
MATCH (p:Person)
OPTIONAL MATCH path = (p)-[:KNOWS]->(friend:Person)
WHERE p.age > 25
UNWIND [path] AS pth
RETURN p.name AS person_name, count(pth) AS friend_count
```
For rows where `path` was null, AGE returned `friend_count = 1` instead of
`0`. Reducing the case to `UNWIND [null]` reproduced the same incorrect
counting behavior.
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