YGY-001 opened a new issue, #2596:
URL: https://github.com/apache/age/issues/2596
## Environment
- Apache AGE `1.8.0`, PostgreSQL `18.6`
- Docker image: `apache/age:release_PG18_1.8.0`
## Reproduction
Create two initially unlabeled nodes in each of two clean graphs:
```sql
LOAD 'age';
SET search_path = ag_catalog, public;
SELECT ag_catalog.create_graph('age_repro24_left');
SELECT *
FROM ag_catalog.cypher('age_repro24_left', $$
CREATE (), ()
$$) AS (v agtype);
SELECT ag_catalog.create_graph('age_repro24_right');
SELECT *
FROM ag_catalog.cypher('age_repro24_right', $$
CREATE (), ()
$$) AS (v agtype);
```
### Baseline — `age_repro24_left`
```sql
SELECT *
FROM ag_catalog.cypher('age_repro24_left', $$
MATCH (n)
DETACH DELETE n
MERGE (:New)
RETURN count(*) AS rows
$$) AS (rows agtype);
```
### Row-materialized variant — `age_repro24_right`
```sql
SELECT *
FROM ag_catalog.cypher('age_repro24_right', $$
MATCH (n)
WITH {n: n} AS row
WITH collect(row) AS rows
UNWIND rows AS row
WITH row.n AS n
DETACH DELETE n
MERGE (:New)
RETURN count(*) AS rows
$$) AS (rows agtype);
```
The `collect`/`UNWIND` block preserves the two input rows and their bindings;
it materializes the earlier `MATCH` result before the later writes.
## Expected and actual
The initial `MATCH` should bind the two nodes that exist when that clause is
evaluated. The later `MERGE` must not add another row to that
already-completed
scan. Both queries should therefore return `2`.
On AGE 1.8.0 / PostgreSQL 18.6:
```text
baseline: 3 rows
barrier: 2 rows
```
The official Cypher clause-composition documentation states that a clause
cannot observe writes made by a later clause and notes that a `MATCH` before
`CREATE` does not find the node created later in the query: [Neo4j Cypher
clause
composition](https://neo4j.com/docs/cypher-manual/current/clauses/clause-composition/).
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