`coalesce()` with a boolean expression and a constant literal fails: COALESCE types boolean and agtype cannot be matched

[hkjiang26]

Bug description

Writing a Cypher query that passes a boolean expression together with a constant literal to coalesce() — e.g. coalesce(1 = 1, false) — makes AGE generate a PostgreSQL COALESCE whose argument types do not match: the boolean comparison is compiled to a native boolean, while the constant branch remains agtype. PostgreSQL rejects the whole query at parse time with error 42804 COALESCE types boolean and agtype cannot be matched. The statement is valid Cypher (it returns a boolean 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:

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

SELECT * FROM cypher('graph_test', $$ RETURN coalesce(1 = 1, false) AS c $$) AS (a agtype);

ERROR:  COALESCE types boolean and agtype cannot be matched
LINE 1: ...OM cypher('graph_test', $$ RETURN coalesce(1 = 1, false) AS ...
                                                             ^

The same error also occurs:

• when the boolean branch is a node-property comparison, e.g. MATCH (n) RETURN coalesce(n.id = 42, false);
• when the constant branch is true or null instead of false;
• with aggregates, e.g. RETURN coalesce(avg(x), 0) (message: COALESCE types double precision and agtype cannot be matched).

Only coalesce calls whose arguments are all agtype already work, e.g. RETURN coalesce(42, 0) or MATCH (n) RETURN coalesce(n.id, 0).

Expected behavior

The statement is valid Cypher: both arguments of coalesce() are booleans (or coercible to a common type), so it should run successfully and return true (the first non-null argument). A query mixing a comparison with a constant is routine and must not be rejected with a PostgreSQL type-coercion error. The bug is in AGE's SQL generation: the constant branch should be coerced to agtype so the generated COALESCE type-checks.

Environment

• Version: 1.8.0 (official apache/age:1.8.0 Docker image)
• PostgreSQL: 18.1 (Debian 18.1-1.pgdg13+2), x86_64