MariaDB [(none)]> select db from mysql.db where db='test\\_%';
+---------+
| db      |
+---------+
| test\_% |
+---------+
1 row in set (0.00 sec)

MariaDB [(none)]> select db from mysql.db where db='test\_%';
+---------+
| db      |
+---------+
| test\_% |
+---------+
1 row in set (0.00 sec)