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)
I can reproduce this on HEAD. The following commit introduced this incorrect result:
commit cb8e50a4a09fe541e32cd54ea90a97f2924121a1
Author: Tom Lane <
tgl@sss.pgh.pa.us>
Date: Fri Aug 30 12:42:12 2024 -0400
Avoid inserting PlaceHolderVars in cases where pre-v16 PG did not.
The calling contain_nonstrict_functions() returned false when checking JsonConstructorExpr.
postgres=# SELECT json_array(3, 2, NULL);
json_array
------------
[3, 2]
(1 row)
The JsonConstructorExpr seems non-strict function.
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 6f0b338d2cd..5ef364b7f7c 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -1115,6 +1115,8 @@ contain_nonstrict_functions_walker(Node *node, void *context)
return true;
if (IsA(node, BooleanTest))
return true;
+ if (IsA(node, JsonConstructorExpr))
+ return true;
I added the above codes, then the query returned the correct result.
I didn't dig more the details. Any thought?
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