SQL join: selecting last records from duplicates - mysql

Question

I am working on python project "Linux Server Monitor". When you load monitoring website you create your servers and table look like this:
Servers:
+-----------+-----------+---------+-------------+
| server_id | auth_code | user_id | server_name |
+-----------+-----------+---------+-------------+
| 0 | xyz123 | 1 | My Server 1 |
| 1 | aabb | 45 | BlaBlaUser |
| 2 | asdfh1 | 1 | My Server 5 |
+-----------+-----------+---------+-------------+
After the server is created, you start python script and it starts to upload monitoring data to this table (where all data is stored, from all users):
Monitoring Data:
+----+-----------+---------+---------+------------+-----------------+------------------+
| id | auth_code | user_id | os_name | os_version | external_ip | some_other_table |
+----+-----------+---------+---------+------------+-----------------+------------------+
| 0 | aabb | 45 | Ubuntu | 16.04 | 77.88.99.100 | dynamic data |
| 1 | aabb | 45 | Ubuntu | 16.04 | 77.88.99.100 | dynamic data 2 |
| 2 | aabb | 45 | Ubuntu | 16.04 | 10.10.10.10 | dynamic data 3 |
| 3 | xyz123 | 1 | Fedora | 27 | 92.94.95.99 | different data 1 |
| 4 | xyz123 | 1 | Fedora | 27 | 92.94.95.99 | different data 2 |
| 5 | xyz123 | 1 | Fedora | 27 | 92.94.95.99 | different data 3 |***
| 6 | asdfh1 | 1 | CentOS | 7 | 5.5.5.5 | some new data 1 |
| 7 | asdfh1 | 1 | CentOS | 7 | 5.5.5.5 | some new data 2 |
| 8 | asdfh1 | 1 | CentOS | 7 | 2.2.2.2 | some new data 3 |###
+----+-----------+---------+---------+------------+-----------------+------------------+
I want to join first and second table to show user "important" information like this:
Your Active Servers:
+-----------+-------------+---------+------------+-----------------+
| server_id | server_name | os_name | os_version | external_ip |
+-----------+-------------+---------+------------+-----------------+
| 0 | My Server 1 | Fedora | 27 | 92.94.95.99 |***
| 2 | My Server 5 | CentOS | 7 | 2.2.2.2 |###
+-----------+-------------+---------+------------+-----------------+
If I join first and second table by user_id it will load duplicates too but I want only last inserted record of that particular user's server. In this case on last record "external_ip" of one server changed but other one remained the same (marked with *** and ###).

Answer 1

you could use an inner join on subselect for the max id for user, server on monitorig
select s.server_id, s.server_name, m.os_name, m.os_version, m.external_ip
from servers s
inner join Monitoring m on m.user_id = s.user_id and s.auth_code = m.auth_code
inner join (
select max(id) max_id, user_id, os_name, os_version
from Monitoring
group by user_id, os_name, os_version
) t on t.max_id = m.id
where user_id = 1