`drop user` failed when `set names gbk`

[Defined2014]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

set names gbk;
create user '测';
drop user '测';

create user '一';
drop user '一';

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

No error

3. What did you see instead (Required)

Failed

ERROR 1396 (HY000): Operation DROP USER failed for 娴?@%

4. What is your TiDB version? (Required)

There are two problems:

• syntax error if character_set_client is gbk #30565
• https://github.com/pingcap/tidb/blob/master/executor/simple.go#L1359-L1370, Transform '测' -> '娴?' -> 0xE5A8B43F ('濞?')

[Defined2014]

/feature developing

[Defined2014]

/severity major

[Defined2014]

/assign

[github-actions]

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