What's the best way to get data for sampling points within a timeframe

I'm looking for some advice how to set up a set of queries which check for an aggregated value for sampling points within a time period. This should run at an IQ-server, so maybe not this many procedure calls would be cool ;) I had a look into the windowing feature. I think it might only work for aggregate data for timeframe, not at a sampling point. So having this scenario: I have a list of items with a start and an end date. I need to collect a sum of processes active at a current time. It's not about system processes, but more about something like how many craftsman were working at a given time. Imagine tables like this (I've modified the example a little to leave out boring parts.... so might it not run perfectly) create table items ( id int ot null default autoincrement, "Type" integer, TimeStampStart datetime null, TimeStampend datetime null ) is currently used by this queryset: create table #Processes( "Type" integer, "timestamp" "datetime" null, "Sum" integer null ) set @date = '20120303' while @date = @date group by "Type" set @date = "dateadd"("ss",3600,@date) end select * from #Processes; This might not the best way of doing it. So I'm looking for a better approach ;)