There can be several reasons why selecting database may fail (non-existing database name for example). I think only ER_DBACCESS_DENIED_ERROR would fit into "access denied" category, and thus should be handled as other access-denieds
Good point. Currently, MariaDB does raise ER_DBACCESS_DENIED_ERROR if the named database doesn't exist. Would you consider that a bug too? For example:
[ec2-user@ip-172-30-0-198 ~]$ sudo mysql -u root --execute="SHOW DATABASES"
|
+--------------------+
|
| Database |
|
+--------------------+
|
| db1 |
|
| information_schema |
|
| mysql |
|
| performance_schema |
|
| test |
|
+--------------------+
|
[ec2-user@ip-172-30-0-198 ~]$ mysql -u bob -ppassword --execute="SHOW GRANTS"
|
+------------------------------------------------------------------------------------------------------------+
|
| Grants for bob@localhost |
|
+------------------------------------------------------------------------------------------------------------+
|
| GRANT USAGE ON *.* TO 'bob'@'localhost' IDENTIFIED BY PASSWORD '*2470C0C06DEE42FD1618BB99005ADCA2EC9D1E19' |
|
| GRANT PROXY ON 'dba'@'localhost' TO 'bob'@'localhost' |
|
| GRANT PROXY ON 'app1_dba'@'localhost' TO 'bob'@'localhost' |
|
+------------------------------------------------------------------------------------------------------------+
|
[ec2-user@ip-172-30-0-198 ~]$ mysql -u bob -ppassword doesnotexist
|
ERROR 1044 (42000): Access denied for user 'bob'@'localhost' to database 'doesnotexist'
|
[ec2-user@ip-172-30-0-198 ~]$ mysql -u bob -ppassword db1
|
ERROR 1044 (42000): Access denied for user 'bob'@'localhost' to database 'db1'
|
I only read code, I did not try it 
According to code, ER_WRONG_DB_NAME, ER_BAD_DB_ERROR may also be thrown, as well as some kind of "out of memory" inside my_strndup() in mysql_change_db() in sql_db.cc
I think ER_BAD_DB_ERROR would show up, if permissions are ok, but database directory does not exist, which is quite likely rare occasion.