Simultaneous calls

Question

I\'m trying to calculate the number of simultaneous calls at the time a particular call is made by looking at the datetime ranges. My query works, but takes ~10 minutes to p

Answer 1

Use SQL like this to get a list of start/end events...

Select CallStart, 1 As CallCount From #rg
Union All
Select CallEnd, -1 From #rg
Order By CallStart

...then treat this as a simple running totals problem, which is solved differently depending upon your SQL Server version or can be easily addressed in code if that's an option.

Answer 2

This should do it:

 ;WITH cteCallEvents As
 (
        SELECT *, CallStart As EventTime, 1 As EventType FROM #rg r
    UNION ALL
        SELECT *, CallEnd   As EventTime, 0 As EventType FROM #rg r
 )
 , cteCallCounts As
 (
    SELECT *,
        ROW_NUMBER() OVER(Order By EventTime) as EventCount,
        ROW_NUMBER() OVER(Partition By EventType Order By EventTime) as TypeCount
    FROM cteCallEvents
 )
 SELECT *,
    2*TypeCount - EventCount  As OpenCalls
FROM    cteCallCounts
WHERE   EventType = 1

It should take a couple of seconds at most. Should work on any SQL Server 2005+.