Steps to reproduce:

1. Install Zabbix server 4.2.x or older version
2. Enable MySQL monitoring
3. Upgrade Zabbix server to 4.4.x in place
4. See MySQL monitoring corrupted

Result:

# zabbix_get -s 1.2.3.4 -k mysql.ping
mysqladmin: connect to server at '-P' failed
error: 'Unknown MySQL server host '-P' (-2)'
Check that mysqld is running on -P and that the port is 3306.
You can check this by doing 'telnet -P 3306'

Expected:
Success MySQL monitoring without a need to manually modify templates in Zabbix-server.

Older versions of Zabbix server use the following format:

zabbix_get -s 1.2.3.4 -k mysql.ping

and Zabbix 4.4 uses format as the following:

zabbix_get -s 1.2.3.4 -k "mysql.ping[localhost,3306]"

Zabbix documentation should mention the changes and warn users about it.

Zabbix template should be upgraded to use new-way calls to Zabbix-agents.

Regards,
Alex.