You can measure almost any count or aggregation over a data column (such as an average or median), metrics that you create, or metrics that Scuba creates automatically when you create named expressions (specifically, when you create sessions and funnels).
Use the Interactive Query Builder to specify a top-level aggregation function using the Measure controls. Time and Table views support multiple simultaneous measures in the results.
A physical column listed here causes the column to be scanned and aggregated. A virtual column listed here is interpreted either during the scan (derived and lookup table columns) or during prior scans (custom metrics). The query planner minimizes the number of required scans and collapses the work as much as possible.