Custom SQL Query for SSL-VPN usage in the FortiAnalayzer

We want to generate a custom rapport for the SSL-VPN usage using the FortiAnalayzer.

We have one appliance dedicated to the SSL-VPN usage. All our customers are using this same appliance and each customer is in the dedicated VDOM.

We want a rapport that show to us the following information:

-        The average per month of users who used the SSL-VPN, for the previous year and for each customer (VDOM).

For this, we need a custom SQL query to be used in the Dataset. Can you please suggest such query ?