Lower and Upper function wrong result

[gengliqi]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

mysql> create table t(a varchar(32)) DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
Query OK, 0 rows affected (0.19 sec)

mysql> alter table t set tiflash replica 1;
Query OK, 0 rows affected (0.17 sec)

mysql> insert into t values('ı'),('İ');
Query OK, 2 rows affected (0.01 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select a,upper(a),lower(a) from t;
+------+----------+----------+
| a    | upper(a) | lower(a) |
+------+----------+----------+
| ı    | I�        | ı        |
| İ    | İ        | i�        |
+------+----------+----------+
2 rows in set (0.01 sec)

2. What did you expect to see? (Required)

mysql> select a,upper(a),lower(a) from t;
+------+----------+----------+
| a    | upper(a) | lower(a) |
+------+----------+----------+
| ı    | I        | ı        |
| İ    | İ        | i        |
+------+----------+----------+
2 rows in set (0.01 sec)

3. What did you see instead (Required)

mysql> select a,upper(a),lower(a) from t;
+------+----------+----------+
| a    | upper(a) | lower(a) |
+------+----------+----------+
| ı    | I�        | ı        |
| İ    | İ        | i�        |
+------+----------+----------+
2 rows in set (0.01 sec)

4. What is your TiFlash version? (Required)

master

[XuHuaiyu]

This issue does not need to be classified as severity/critical.
The problematic characters are rare and occur very infrequently in normal business scenarios.

I'll change the severity label to severity/major.