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* BUG #19004: Incorrect lowercasing of word-final Greek capital Sigma (Σ)
@ 2025-07-31 03:06 PG Bug reporting form <noreply@postgresql.org>
2025-07-31 07:39 ` Re: BUG #19004: Incorrect lowercasing of word-final Greek capital Sigma (Σ) John Naylor <johncnaylorls@gmail.com>
0 siblings, 1 reply; 2+ messages in thread
From: PG Bug reporting form @ 2025-07-31 03:06 UTC (permalink / raw)
To: pgsql-bugs@lists.postgresql.org; +Cc: 221250180@smail.nju.edu.cn
The following bug has been logged on the website:
Bug reference: 19004
Logged by: Bosheng Peng
Email address: 221250180@smail.nju.edu.cn
PostgreSQL version: 17.5
Operating system: windows with docker
Description:
When applying UPPER() to the Greek word 'κόσμος', PostgreSQL returns
'ΚΌΣΜΟΣ'. However, applying LOWER() to that result returns 'κόσμοσ' instead
of the original 'κόσμος'.
According to wikipedia (https://en.wikipedia.org/wiki/Sigma), there are two
forms of lowercase for Greek capital Sigma (Σ):
- If Σ is at the end of a word, it should lowercase to ς
- If Σ is in the middle of a word, it should lowercase to σ
How to repeat:
```sql
SELECT LOWER(UPPER('κόσμος'));
-- Expected: 'κόσμος'
-- Actual: 'κόσμοσ'
```
^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: BUG #19004: Incorrect lowercasing of word-final Greek capital Sigma (Σ)
2025-07-31 03:06 BUG #19004: Incorrect lowercasing of word-final Greek capital Sigma (Σ) PG Bug reporting form <noreply@postgresql.org>
@ 2025-07-31 07:39 ` John Naylor <johncnaylorls@gmail.com>
0 siblings, 0 replies; 2+ messages in thread
From: John Naylor @ 2025-07-31 07:39 UTC (permalink / raw)
To: 221250180@smail.nju.edu.cn; pgsql-bugs@lists.postgresql.org
On Thu, Jul 31, 2025 at 1:50 PM PG Bug reporting form
<noreply@postgresql.org> wrote:
> When applying UPPER() to the Greek word 'κόσμος', PostgreSQL returns
> 'ΚΌΣΜΟΣ'. However, applying LOWER() to that result returns 'κόσμοσ' instead
> of the original 'κόσμος'.
Hi,
For built-in collations, context-sensitive case mappings are a
forthcoming feature which will be available in PG18 later this year,
with the pg_unicode_fast collation:
CREATE TABLE example (
a text COLLATE PG_UNICODE_FAST,
b text COLLATE PG_C_UTF8
);
INSERT INTO example VALUES ('κόσμος', 'κόσμος');
SELECT LOWER(UPPER(a)), LOWER(UPPER(b)) FROM example;
lower | lower
--------+--------
κόσμος | κόσμοσ
(1 row)
--
John Naylor
Amazon Web Services
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