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UNWIND [null] may produce a row whose value prints as null, but count(x) still counts it as 1. #2383
Description
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
psqlinside the Docker container
What data setup do we need to do?
No graph data is required beyond creating an empty graph:
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?
SELECT * FROM cypher('fuzz_graph', $$
UNWIND [null] AS x
RETURN count(x) AS c
$$) AS (c agtype);Returned result on AGE:
c
---
1
Expected behavior
The result should be:
c
---
0
Neo4j returns 0 for the equivalent Cypher query:
UNWIND [null] AS x
RETURN count(x) AS cEnvironment (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:
- Plain
count(null)behaves correctly:
SELECT * FROM cypher('fuzz_graph', $$
RETURN count(null) AS c
$$) AS (c agtype);Observed result:
0
WITH null AS x RETURN count(x)also behaves correctly:
SELECT * FROM cypher('fuzz_graph', $$
WITH null AS x
RETURN count(x) AS c
$$) AS (c agtype);Observed result:
0
UNWIND [null] AS x RETURN xshows that the produced row is indeednull:
SELECT * FROM cypher('fuzz_graph', $$
UNWIND [null] AS x
RETURN x
$$) AS (x agtype);Observed result:
null
A larger differential-testing case first exposed this via:
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_countFor 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.
Activity
crprashant commentedon Apr 22, 2026
Hi! I'd like to work on this. Could a maintainer please assign it to me?
Initial hypothesis:
UNWINDmay be emitting an agtypenullvalue rather than a true SQL NULL, so the null-check inside thecount()aggregate doesn't trigger. The reporter's control cases confirmWITH null AS x RETURN count(x)works correctly, which suggests the divergence is specifically in UNWIND's row materialization path. I'll reproduce locally, trace the executor output, compare against theWITHpath, and follow up with a fix proposal plus a regression test.Fix UNWIND [null] causing count() to miscount null rows (apache#2383)
Fix UNWIND [null] causing count() to miscount null rows (apache#2383)
gregfelice commentedon Jul 3, 2026
@jrgemignani — we have two open PRs fixing this bug via opposite approaches, and they conflict, so whichever merges first forces a rework of the other. Flagging for a maintainer call on direction before either author spends more effort (e.g. #2406 currently needs a rebase I've just asked for):
#2411 (@crprashant) — narrow. Adds a separate
age_unwindSRF and repoints onlytransform_cypher_unwindto it;age_unnestis untouched. Low blast radius, no risk to list comprehensions / predicate functions. Deliberately fixes only this issue (#2383) — it leaves the sibling list-comprehension null bug (#2393) and thesingle()/ predicate three-valued-logic quirk unfixed, since those callers still rely onagtype_null > agtype_integerbeing truthy. (Currently conflicting + no green CI run.)#2406 (@MuhammadTahaNaveed) — root-cause. Fixes
age_unnestin place (emit SQL NULL forAGTV_NULL) and rewrites the predicate-function 3VL, so it fixes #2383 + #2393 +single()together and makesnull > 0yieldnullper openCypher instead of truthy. Larger surface, but I've reviewed it and the approach is sound; it needs a rebase + two small tidy-ups (INT8PASSBYVAL, a comment).They're mutually redundant on the
age_unnest/UNWIND path — we should merge one and close the other.My lean is #2406 as the more correct end state (fixes the whole null-handling family, not just the UNWIND symptom), with #2411 as the lower-risk fallback if we'd rather ship the narrow fix now and defer the 3VL rework. Your call on the direction — I'll shepherd whichever you pick to green + approval.
Propagate null through unnest and single() three-valued logic (apache…
Propagate null through unnest and single() three-valued logic (#2406)
Propagate null through unnest and single() three-valued logic (#2406)