What is the syntax of the select statement to show the number of distinct
volumes used by each stgpool for each node.  The desired output would be
something like:

Node_Name   StgPool_Name  Count
---------   ------------  ------
yakima      backupcopy         5
yakima      backuptape         3
yakima      arccopy            7
yakima      arctape            6
olympia     backupcopy        23
olympia     backuptape        15
...