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help / color / mirror / Atom feedFrom: Richard Guo <rguo@postgresql.org>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: Fix const-folding of JSON constructors inside a simple CASE
Date: Mon, 14 Sep 2026 08:09:57 +0000
Message-ID: <E1x61lF-00000000G0t-27VF@gemulon.postgresql.org> (raw)
Fix const-folding of JSON constructors inside a simple CASE
A JSON constructor with a RETURNING clause uses a CaseTestExpr as the
placeholder for its result in the coercion expression. When such a
constructor appears in a WHEN clause of a simple CASE whose test
expression is a constant, eval_const_expressions substituted that
constant for the placeholder, so the coercion produced the CASE's test
value instead of the constructor's result. For instance,
CASE 'x' WHEN JSON_OBJECT('a': 'b' RETURNING text) THEN 1 ELSE 0 END
evaluated to 1.
To fix, keep case_val out of scope while simplifying the coercion, as
is already done for the elemexpr of an ArrayCoerceExpr.
Back-patch to v16, where the SQL/JSON constructor functions were
introduced.
Author: Richard Guo <guofenglinux@gmail.com>
Discussion: https://postgr.es/m/CAMbWs48A=VCFbteTkuCoknO1_0-Cu0aMBT0M07dm7vj1QyixDg@mail.gmail.com
Backpatch-through: 16
Branch
------
REL_17_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/23088673d311ae274069f7147cf280ee2540aeea
Modified Files
--------------
src/backend/optimizer/util/clauses.c | 35 ++++++++++++++++++++++++++++++++++-
src/include/nodes/primnodes.h | 10 +++++-----
src/test/regress/expected/sqljson.out | 7 +++++++
src/test/regress/sql/sqljson.sql | 3 +++
4 files changed, 49 insertions(+), 6 deletions(-)
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To: pgsql-committers@postgresql.org
Cc: rguo@postgresql.org, pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Fix const-folding of JSON constructors inside a simple CASE
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