Bug #107645 the cast function gets an incorrect result if with wrong encoding

• Submitted: 24 Jun 2022 3:00
• Modified: 24 Jun 2022 4:51
• Reporter: x j
• Status: Verified
• Category: MySQL Server: DML
• Severity: S3 (Non-critical)
• Version: 5.7.38, 8.0.29
• OS: Any
• CPU Architecture: Any

[24 Jun 2022 3:00] x j

Description:
the cast function gets an incorrect result if wrong binary literal to char

How to repeat:
mysql> select cast(0x80 as char);
+--------------------+
| cast(0x80 as char) |
+--------------------+
| �                   |
+--------------------+
1 row in set (0.00 sec)

I think it should report an error like `cannot convert xxx from binary to utf8mb4`
or just return NULL, but not an unknowing character

[24 Jun 2022 4:51] MySQL Verification Team

Hello x j,

Thank you for the report and test case.

regards,
Umesh

[28 Jun 2022 13:48] huahua xu

Hi,

There is not any conversion needed wher the cast function converts xxx from binary to other character set.

mysql>  select convert(0x80 USING utf8mb4);
+-----------------------------+
| convert(0x80 USING utf8mb4) |
+-----------------------------+
| NULL                        |
+-----------------------------+

mysql> show warnings;
+---------+------+----------------------------------------+
| Level   | Code | Message                                |
+---------+------+----------------------------------------+
| Warning | 1300 | Invalid utf8mb4 character string: '80' |
+---------+------+----------------------------------------+

the convert function is ok for you?