Postgres 14

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Help with an interesting Postgres question: Why isn't an Index Only Scan used on a partition accessed via the parent table?.

CREATE COLLATION ithelp1010_weird (
   PROVIDER = 'icu',
   LOCALE = 'en-u-kr-space-latn-digit'
);

create table it221010 (
  id int primary key
, test text
);

insert into it221010 values
(1, 'AB'),(2, '12'), (3, 'BX'), (4, NULL), (5, '34'), (6, '');

CREATE COLLATION

CREATE TABLE

INSERT 0 6

select *
  from it221010;

id
test

1
AB

2
12

3
BX

4
null

5
34

6

SELECT 6

select *
  from it221010
 order by test COLLATE ithelp1010_weird nulls first;

id
test

4
null

6

1
AB

3
BX

2
12

5
34

SELECT 6

id	test
1	AB
2	12
3	BX
4	null
5	34
6

id	test
4	null
6
1	AB
3	BX
2	12
5	34