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 - GPL

Copyright (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 - GPL

Copyright (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)