From: PG Bug reporting form <noreply@postgresql.org>
To: pgsql-bugs@lists.postgresql.org
Cc: 221250180@smail.nju.edu.cn
Subject: BUG #19004: Incorrect lowercasing of word-final Greek capital Sigma (Σ)
Date: Thu, 31 Jul 2025 03:06:10 +0000
Message-ID: <19004-05eb4ef0b05f4aeb@postgresql.org> (raw)
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'
```
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Subject: Re: BUG #19004: Incorrect lowercasing of word-final Greek capital Sigma (Σ)
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