From: Eric Ridge <eebbrr@gmail.com>
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Subject: pg18 bug?  SELECT query doesn't work
Message-Id: <7900964C-F99E-481E-BEE5-4338774CEB9F@gmail.com>
Date: Tue, 6 Jan 2026 10:22:23 -0500
To: pgsql-general <pgsql-general@postgresql.org>
Archived-At: <https://www.postgresql.org/message-id/7900964C-F99E-481E-BEE5-4338774CEB9F%40gmail.com>
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Hi all!

I ran into a situation where a query that worked just fine on pg15 fails =
on pg18.1 with an ERROR. =20

I've compiled pg18.1 from source:

# select version();
                                                      version            =
                                          =20
=
--------------------------------------------------------------------------=
-----------------------------------------
 PostgreSQL 18.1 on aarch64-apple-darwin24.4.0, compiled by Apple clang =
version 17.0.0 (clang-1700.0.13.5), 64-bit
(1 row)

$ pg_config --configure
 '--prefix=3D/path/to/pg18' '--with-pgport=3D5418' '--enable-debug' =
'--enable-cassert' 'CPPFLAGS=3D -DUSE_ASSERT_CHECKING=3D1 =
-DRANDOMIZE_ALLOCATED_MEMORY=3D1 ' =
'PKG_CONFIG_PATH=3D/opt/homebrew/opt/icu4c/lib/pkgconfig' 'CFLAGS=3D-O0 =
-g' 'CXXFLAGS=3D-I/opt/homebrew/include'


Here's a reduced test case:

drop table if exists wth;
create table wth (id serial8, json_data json);
insert into wth (json_data) values ('[{"animal": "cats"}, {"animal": =
"dogs"}]');

-- this ERRORs on pg18
select animal
from (select upper(json_array_elements(json_data) ->> 'animal') animal, =
count(*) from wth group by 1) x
where animal ilike 'c%';


On pg15 I get the expected result of:

 animal =20
--------
 CATS
(1 row)


On pg18 I'm presented with:

ERROR:  set-valued function called in context that cannot accept a set
LINE 1: select animal from (select upper(json_array_elements(json_da...

With pg18 I messed around with rewriting it and discovered another =
inconsistency:

# with animals as (
select animal
from (select upper(json_array_elements(json_data) ->> 'animal') animal, =
count(*) from wth group by 1) x)
select * from animals where animal ilike 'c%';
ERROR:  set-valued function called in context that cannot accept a set
LINE 3: from (select upper(json_array_elements(json_data) ->> 'anima...

v/s

# with animals as MATERIALIZED (
select animal
from (select upper(json_array_elements(json_data) ->> 'animal') animal, =
count(*) from wth group by 1) x)
select * from animals where animal ilike 'c%';

 animal =20
--------
 CATS
(1 row)

I'd expect both those queries to return "CATS", in addition to the =
original query that worked on (at least) pg15.

Just thought I'd bring this to y'alls attention.

Thanks and happy 2026!

eric