【 TiDB 使用环境】生产环境 /测试/ Poc
【 TiDB 版本】
【复现路径】做过哪些操作出现的问题
【遇到的问题：问题现象及影响】
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问题简述：
tidb 7.5中，测试语句在utf8mb4字符集下执行报错，但是latin1下正常，表现与mysql/mariadb不一致，具体示例如下，请参考。
TiDB
测试用例如下，
-- tidb 7.5, utf8mb4 (default), 报错error
set names utf8mb4;
select cast(compress('b') as char);
-- tidb 7.5, latin, 正常返回
set names latin1;
select cast(compress('b') as char);
output:
MySQL [test]> select version();
+--------------------+
| version() |
+--------------------+
| 8.0.11-TiDB-v7.5.0 |
+--------------------+
1 row in set (0.001 sec)
MySQL [test]> set names utf8mb4;
Query OK, 0 rows affected (0.000 sec)
MySQL [test]> select cast(compress('b') as char);
ERROR 3854 (HY000): Cannot convert string '
MySQL [test]> set names latin1;
Query OK, 0 rows affected (0.000 sec)
MySQL [test]> select cast(compress('b') as char);
+-----------------------------+
| cast(compress('b') as char) |
+-----------------------------+
| x▒J ▒▒ c c |
+-----------------------------+
1 row in set (0.001 sec)
MySQL
对比mysql，8.2/8.0 表现一致，该语句均可返回结果，只是在utf8mb4下返回null和warn，而不是error。
MySQL 5.7 中，utf8mb4/latin 均可正常返回结果。
- 8
mysql> select version();
+-----------+
| version() |
+-----------+
| 8.0.32 |
+-----------+
1 row in set (0.00 sec)
mysql> set names utf8mb4;
Query OK, 0 rows affected (0.00 sec)
mysql> select cast(compress('b') as char);
+-----------------------------+
| cast(compress('b') as char) |
+-----------------------------+
| NULL |
+-----------------------------+
1 row in set, 1 warning (0.00 sec)
mysql> show warnings;
+---------+------+--------------------------------------------+
| Level | Code | Message |
+---------+------+--------------------------------------------+
| Warning | 1300 | Invalid utf8mb4 character string: '9C4B02' |
+---------+------+--------------------------------------------+
1 row in set (0.00 sec)
mysql> set names latin1;
Query OK, 0 rows affected (0.00 sec)
mysql> select cast(compress('b') as char);
+-----------------------------+
| cast(compress('b') as char) |
+-----------------------------+
| x▒K c c |
+-----------------------------+
1 row in set (0.00 sec)
- 5.7
mysql> select version();
+-----------+
| version() |
+-----------+
| 5.7.38 |
+-----------+
1 row in set (0.00 sec)
mysql> set names utf8mb4;
Query OK, 0 rows affected (0.00 sec)
mysql> select cast(compress('b') as char);
+-----------------------------+
| cast(compress('b') as char) |
+-----------------------------+
| x▒K c c |
+-----------------------------+
1 row in set (0.00 sec)
mysql> set names latin1;
Query OK, 0 rows affected (0.00 sec)
mysql> select cast(compress('b') as char);
+-----------------------------+
| cast(compress('b') as char) |
+-----------------------------+
| x▒K c c |
+-----------------------------+
1 row in set (0.00 sec)
MariaDB
在mariadb中，utf8mb4/latin返回结果一致，
MariaDB [(none)]> set names utf8mb4;
Query OK, 0 rows affected (0.002 sec)
MariaDB [(none)]> select cast(compress('b') as char);
+-----------------------------+
| cast(compress('b') as char) |
+-----------------------------+
| x?K c c |
+-----------------------------+
1 row in set, 1 warning (0.369 sec)
MariaDB [(none)]> show warnings;
+---------+------+-------------------------------------------------------------+
| Level | Code | Message |
+---------+------+-------------------------------------------------------------+
| Warning | 1300 | Invalid utf8mb4 character string: '\x9CK\x02\x00\x00c\x00c' |
+---------+------+-------------------------------------------------------------+
1 row in set (0.000 sec)
MariaDB [(none)]> set names latin1;
Query OK, 0 rows affected (0.000 sec)
MariaDB [(none)]> select cast(compress('b') as char);
+-----------------------------+
| cast(compress('b') as char) |
+-----------------------------+
| x▒K c c |
+-----------------------------+
1 row in set (0.000 sec)
MariaDB [(none)]> select version();
+-------------------------------------+
| version() |
+-------------------------------------+
| 10.7.3-MariaDB-1:10.7.3+maria~focal |
+-------------------------------------+
1 row in set (0.000 sec)