我可以在10.6.12上复制：

set @@character_set_connection=utf8mb4;
select '😃' rlike '^[?]+$';

字符串
我想可能跟这个问题有关：
https://jira.mariadb.org/browse/MDEV-11777?jql=project%20%3D%20MDEV%20AND%20text%20~%20%22regexp%22
当字符集为utf8mb4时，REGEXP_REPLACE函数将补充字符（4字节utf8编码）转换为“？”。
但是对danblack的MDEV-32904的响应表明它可能是由于character_set%变量中的不匹配而发生的。例如：

MariaDB [(none)]> show variables like 'character_set_%';
+--------------------------+----------------------------+
| Variable_name            | Value                      |
+--------------------------+----------------------------+
| character_set_client     | utf8mb3                    |
| character_set_connection | utf8mb3                    |
| character_set_database   | utf8mb4                    |
| character_set_filesystem | binary                     |
| character_set_results    | utf8mb3                    |
| character_set_server     | utf8mb4                    |
| character_set_system     | utf8mb3                    |
| character_sets_dir       | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+
8 rows in set (0.001 sec)

MariaDB [(none)]> select hex('😃');
+-------------------------+
| hex('\xF0\x9F\x98\x83') |
+-------------------------+
| F09F9883                |
+-------------------------+
1 row in set (0.000 sec)

MariaDB [(none)]> set @@character_set_connection=utf8mb4;
Query OK, 0 rows affected (0.000 sec)

MariaDB [(none)]> select hex('😃');
+-------------------------+
| hex('\xF0\x9F\x98\x83') |
+-------------------------+
| 3F3F3F3F                |
+-------------------------+
1 row in set (0.000 sec)

MariaDB [(none)]> set names utf8mb4;
Query OK, 0 rows affected (0.000 sec)

MariaDB [(none)]> select hex('😃');
+----------+
| hex('?') |
+----------+
| F09F9883 |
+----------+
1 row in set (0.000 sec)

MariaDB [(none)]>

型