create role devgroup;

select user,host from mysql.user;
+------------------+-----------+
| user             | host      |
+------------------+-----------+
| devgroup         | %         |
| backup           | 127.0.0.1 |
| mysql.sys        | localhost |
| root             | localhost |
+------------------+-----------+

grant all on tempdb.* to devgroup;
Query OK, 0 rows affected (0.07 sec)

create user tom@'127.0.0.1' identified by '123456';
Query OK, 0 rows affected (0.09 sec)grant devgroup to tom@'127.0.0.1';
Query OK, 0 rows affected (0.09 sec)

mysql -h127.0.0.1 -P3306 -utom -p123456
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 16
Server version: 8.0.13 MySQL Community Server - GPLCopyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql> show grants;
+-------------------------------------------+
| Grants for tom@127.0.0.1                  |
+-------------------------------------------+
| GRANT USAGE ON *.* TO `tom`@`127.0.0.1`   |
| GRANT `devgroup`@`%` TO `tom`@`127.0.0.1` |
+-------------------------------------------+
2 rows in set (0.00 sec)

grant root@'127.0.0.1' to tom@'127.0.0.1';
Query OK, 0 rows affected (0.04 sec)

show grants;
+--------------------------------------------------------------+
| Grants for tom@127.0.0.1                                     |
+--------------------------------------------------------------+
| GRANT USAGE ON *.* TO `tom`@`127.0.0.1`                      |
| GRANT `devgroup`@`%`,`root`@`127.0.0.1` TO `tom`@`127.0.0.1` |
+--------------------------------------------------------------+
2 rows in set (0.00 sec)

drop database tempdb;
ERROR 1044 (42000): Access denied for user 'tom'@'127.0.0.1' to database 'tempdb'

set @@global.activate_all_roles_on_login=1;
Query OK, 0 rows affected (0.00 sec)

mysql -h127.0.0.1 -P3306 -utom -p123456
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 18
Server version: 8.0.13 MySQL Community Server - GPLCopyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql> use tempdb;
Database changed
mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| tempdb             |
+--------------------+
5 rows in set (0.01 sec)mysql> drop database tempdb;
Query OK, 0 rows affected (0.09 sec)