Bug #118755 Incorrect lowercasing of word-final Greek capital Sigma (Σ)

• Submitted: 31 Jul 2:04
• Modified: 21 Aug 12:32
• Reporter: Bosheng Peng
• Status: Not a Bug
• Category: MySQL Server: DML
• Severity: S3 (Non-critical)
• Version: 8.0.36, 8.0.43, 8.4.6
• OS: Windows
• CPU Architecture: Any

[31 Jul 2:04] Bosheng Peng

Description:
When applying UPPER() to the Greek word 'κόσμος', MySQL 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'
```

[31 Jul 6:45] MySQL Verification Team

Hello Bosheng Peng,

Thank you for the report and feedback.

regards,
Umesh

[21 Aug 12:32] Norvald Ryeng

Posted by developer:
 
This behavior is correct according to the Unicode 9.0 specification. I'm closing this as not a bug.