When there is no activity to report, some data items cause an empty row (that is, a row with zero values for result data items) to appear in a view, and other data items cause the row to be omitted. The rules controlling whether empty rows appear in a view are:
Server level data items always return a row, even when there is no activity to report.
Views that contain the key data item Process ID or Application Name only report on processes that are active as of the end of the sample period.
Views that contain the key data items Object ID or Stored Procedure ID omit the row when there is no activity to report during the sample period.
Views that contain keys other than those listed in the previous bullets return rows when there is no activity.