Drillable Fields in the Data Settings Tab
Drillable fields provide a way to control what is shown on the search page when Dashboard users drill down on a chart data point. If no drillable fields are specified, then only the metric instance for that datapoint displays on the search page. However, if you specify drillable fields, then more than one metric row is likely to display.
Drillable fields are selected from the group by fields in the metric used for the data point. The selected fields are used in the search criteria that determine what data is returned when the user drills down on a data point.
Only rows in the result set whose drillable group by field values match those of the selected data point's row appear on the search page.
Using fewer drillable fields increases the chances of seeing more than one row on the search page. For example, consider a metric with three group by fields, country, state, and zip code. If you select all three as drillable fields, only the data from the same row as the data point itself is returned. If you select country, all zip codes in the same country as the chart data point's row are returned. If you select country and state, you see all zip codes in the state and country specified in the data point's row.