hkjiang26 opened a new issue, #2512:
URL: https://github.com/apache/age/issues/2512
**Bug description**
Writing a Cypher query that unions a boolean expression with a constant
literal — e.g. `RETURN true IS NOT NULL AS x UNION RETURN true AS x` — makes
AGE generate a PostgreSQL UNION whose branch types do not match: the boolean
expression is compiled to a native `boolean`, while the constant branch remains
`agtype`. PostgreSQL rejects the whole query at parse time with error 42804
`UNION types boolean and agtype cannot be matched`. The statement is valid
Cypher (it returns `true` in Neo4j) and is rejected before producing any result.
**Access method**
- Command line via `psql`, inside the official Docker container
`apache/age:1.8.0`
**Data setup**
No data is required — the error reproduces on an empty graph. Only the graph
itself must exist:
```pgsql
CREATE EXTENSION IF NOT EXISTS age;
LOAD 'age';
SET search_path = ag_catalog, "$user", public;
SELECT create_graph('graph_test');
```
**Configuration**
- None beyond the stock AGE extension. No additional modules (no PostGIS,
etc.), default `search_path` handling as shown above.
**Command that triggers the error**
```pgsql
SELECT * FROM cypher('graph_test', $$ RETURN true IS NOT NULL AS x UNION
RETURN true AS x $$) AS (a agtype);
```
```
ERROR: UNION types boolean and agtype cannot be matched
LINE 1: ... true IS NOT NULL AS x UNION RETURN true AS x
^
```
The same error also occurs:
- with other boolean-only expressions in place of `true IS NOT NULL`, e.g.
`RETURN NOT true AS x UNION RETURN true AS x`, `RETURN true IN [true] AS x
UNION RETURN true AS x`, `RETURN true AND false AS x UNION RETURN true AS x`;
- with an unparenthesized comparison in one branch, e.g. `RETURN 1 = 1 AS x
UNION RETURN true AS x`;
- regardless of which branch holds the boolean expression, e.g. `RETURN true
AS x UNION RETURN true IS NOT NULL AS x` (message: `UNION types agtype and
boolean cannot be matched`);
- without aliases, e.g. `RETURN true IS NOT NULL UNION RETURN true`.
Only unions whose branches are all `agtype` already work, e.g. `RETURN true
AS x UNION RETURN true AS x`. The inferred branch type depends on expression
shape rather than on the Cypher result type:
- `RETURN (1 = 1) AS x UNION RETURN true AS x` succeeds,
- while the same comparison without parentheses (`RETURN 1 = 1 AS x UNION
RETURN true AS x`) fails.
**Environment**
- Version: 1.8.0 (official `apache/age:1.8.0` Docker image)
- PostgreSQL: 18.1 (Debian 18.1-1.pgdg13+2), x86_64
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