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

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From: PG Bug reporting form <noreply@postgresql.org>
To: pgsql-bugs@lists.postgresql.org
Cc: runyuan@berkeley.edu
Date: 2025-09-10T07:14:35Z
Lists: pgsql-bugs

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Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Treat JsonConstructorExpr as non-strict

  2. Avoid inserting PlaceHolderVars in cases where pre-v16 PG did not.

The following bug has been logged on the website:

Bug reference:      19046
Logged by:          Runyuan He
Email address:      runyuan@berkeley.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)