Are you still looking for help on this? If so…
- Do you have the Data-Explorer plugin installed and enabled?
- Can you navigate to
[YourSite]/admin/plugins/explorer?
From there you can create your own data-explorer queries if there isn’t a default one that suits. 
Clicking on the plus sign next to the search box will bring up the ‘add query’ options.
If you need help with the SQL query itself, could you be a little more specific in what data you’re looking to pull out? Is it a post count by category you’re looking for?