BUG #19046: Incorrect result when using json_array() with column reference in subquery combined with RIGHT JOIN

From: PG Bug reporting form <noreply(at)postgresql(dot)org>
To: pgsql-bugs(at)lists(dot)postgresql(dot)org
Cc: runyuan(at)berkeley(dot)edu
Subject: BUG #19046: Incorrect result when using json_array() with column reference in subquery combined with RIGHT JOIN
Date: 2025-09-10 07:14:35
Message-ID: 19046-765b6602b0a8cfdf@postgresql.org
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The following bug has been logged on the website:

Bug reference: 19046
Logged by: Runyuan He
Email address: runyuan(at)berkeley(dot)edu
PostgreSQL version: 18rc1
Operating system: Linux (x86)
Description:

Bug Description:
When using json_array() function with a column reference from table t inside
a subquery, and then performing a RIGHT JOIN with condition FALSE, the
result incorrectly returns [3, 2] instead of the expected NULL value.

Reproducible Example:
CREATE TABLE t(c INT);
INSERT INTO t VALUES (1);

SELECT sub.c FROM
(SELECT json_array(3, 2, t.c) AS c FROM t) AS sub
RIGHT JOIN t ON FALSE;
-- PostgreSQL 16.x: Returns NULL (CORRECT)
-- PostgreSQL 17.6, 17.rc1: Returns [3, 2] (INCORRECT)
-- PostgreSQL 18rc1: Returns [3, 2] (INCORRECT)

SELECT sub.c FROM
(SELECT json_array(3, 2, t.c) AS c FROM t) AS sub;
-- Returns [3, 2, 1] (CORRECT)

SELECT sub.c FROM
(SELECT json_array(3, 2, 1) AS c FROM t) AS sub
RIGHT JOIN t ON FALSE;
-- Returns Null (CORRECT)

Responses

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