Datatable Visualization how to add average vales for two different time range

Hi, I've sample application server log and I've created simple "Uri, Count,Average" Datatable visualization. I need additional column which gives X (defined as one of 15min, 1 week, etc depend on the requirement) minute previous datetime range average values. So that we can easily discover the variation for each Uri. For different type of visualization with datetime range it can be easilly selected but how can it be done for datatable.