I'm also interested in this. I managed to create a custom Dataset with the following query:
When I test this dataset, I get the right answer (great!). But when I try to add the result in a report, I always get the following message in the report: "No matching log data for this report". I have another Dataset which gives me the list of all VPN-SSL connections that occured during the specified timeperiod which is working great, so I can easily work this list in Excel to get the answer by suppressing duplicate entries, but this is very strange. If anyone can help me with this, I'm interested !