crprashant opened a new pull request, #2411:
URL: https://github.com/apache/age/pull/2411
Fixes #2383.
## Problem
Per Neo4j / openCypher semantics, `count()` must ignore nulls. On Apache AGE:
```cypher
UNWIND [null] AS x RETURN count(x) -- returns 1 (buggy), should be 0
```
The control cases already returned the correct `0`:
```cypher
RETURN count(null)
WITH null AS x RETURN count(x)
```
## Root cause
`age_unnest()` in `src/backend/utils/adt/agtype.c` materialized every
top-level array element into a heap tuple with `nulls[0] = false`, even when
the element's `agtype_value.type == AGTV_NULL`. The row that reached `count()`
therefore carried a non-NULL datum wrapping an agtype JSON null, so the
aggregate's strict null check never skipped it.
## Fix
A naïve fix inside `age_unnest()` breaks other callers.
`construct_age_function_name()` in `src/backend/parser/cypher_expr.c` rewrites
`unnest` → `age_unnest`, so list comprehensions and the predicate functions
(`all` / `any` / `none` / `single`) also route through `age_unnest`. Those
callers deliberately rely on the quirk that AGE's `agtype_null >
agtype_integer` evaluates to `agtype_null` (truthy), not SQL NULL. Changing the
SRF broke five `predicate_functions` expected results.
Introduce a dedicated SRF `age_unwind()` with UNWIND-specific null semantics:
- Top-level `AGTV_NULL` elements → SQL NULL rows so null-strict operators
(`count`, `IS NULL`, `WHERE x IS NOT NULL`, …) match `WITH null AS x`.
- Non-null elements are returned unchanged.
- Nested nulls inside arrays/objects are preserved as agtype-null.
`transform_cypher_unwind()` is the only call site changed from `age_unnest`
to `age_unwind`. List comprehensions and predicate functions continue to use
`age_unnest` and their behavior is untouched.
## Before / after
```text
-- before
UNWIND [null] AS x RETURN count(x) -- 1
UNWIND [1, null, 2, null, 3] AS x RETURN count(x) -- 5
UNWIND [null] AS x RETURN x IS NULL -- false
-- after
UNWIND [null] AS x RETURN count(x) -- 0 ✓
UNWIND [1, null, 2, null, 3] AS x RETURN count(x) -- 3 ✓
UNWIND [null] AS x RETURN x IS NULL -- true ✓
```
## Regression tests (`regress/sql/cypher_unwind.sql`)
- `UNWIND [null] RETURN count(x) = 0`
- `UNWIND [1, null, 2, null, 3] RETURN count(x) = 3`
- `UNWIND [null] RETURN x IS NULL`
- `UNWIND [1, null, 2] WITH x WHERE x IS NOT NULL RETURN count(x) = 2`
- `UNWIND [null] RETURN count(*) = 1` (row still produced)
- `UNWIND [[null], {k: null}] RETURN count(x) = 2` (nested nulls preserved)
- `UNWIND [null] RETURN x` — asserts the row value itself is SQL NULL
## Files changed
- `src/backend/utils/adt/agtype.c` — new `age_unwind` SRF
- `src/backend/parser/cypher_clause.c` — UNWIND calls `age_unwind`
- `sql/agtype_typecast.sql` — declare `age_unwind`
- `age--1.7.0--y.y.y.sql` — add `age_unwind` for in-place upgrades
- `regress/sql/cypher_unwind.sql` + `regress/expected/cypher_unwind.out`
## Test results
`make installcheck` with PostgreSQL 18 on Ubuntu 24.04:
- **32/33 tests pass.**
- `age_upgrade` fails identically on `apache/age` master `HEAD`
(pre-existing, unrelated; same `age_prepare_pg_upgrade already exists` error).
- `cypher_unwind`, `predicate_functions`, `list_comprehension` all pass.
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