In the visual below, we needed to A) get all of the averages across all hours, B) find the minimum average of these, and C) compare the rest of the averages to the minimum average. Custom SQL as part of the initial Tableau connection is the best solution here.
In the example below, the client wanted to see - for each utility registrant and each hour of the day - the averages of energy use, but also wanted to see the various averages as compared to the lowest average (I.E. the min of the averages) This solution also allows us to see percentage bands above this minimum. Plus, if you click on a bar segment you can see the exact percentage above the minimum. Nifty!