There doesn't appear to be much information on how to use aggregate functions for ServiceNow, after glancing through the ServiceNow wiki. There are examples of how to use some of the aggregate functions (i.e. SUM, AVG, COUNT, MIN, MAX) with "having" and "group by" clauses. Here's a link to the wiki that describes aggregates and provides examples:
http://wiki.servicenow.com/index.php?title=Direct_Web_Service_API_Functions
The in-app help for the ServiceNow app provides an example of how to use aggregates within Splunk. Note that you will also need to activate the Aggregate Web Services Plug-In in your ServiceNow portal:
http://wiki.servicenow.com/index.php?title=Activating_ServiceNow_Plugins
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