This is my attempt, it works on a 24 hour widow and im sure theres a better way of doing it

CREATE TABLE #Hist

(

CallDateTime DateTime

,HistId int

)

Insert into #Hist

VALUES ('2013-02-01 06:14:41.000',2671058)

,('2013-02-01 07:02:15.000', 2671057)

,('2013-02-01 07:06:41.000', 2671059)

,('2013-02-01 07:07:20.000', 2671069)

,('2013-02-01 07:22:57.000', 2671068)

,('2013-02-01 07:38:15.000', 2671067)

,('2013-02-01 07:42:48.000', 2671066)

,('2013-02-01 07:53:47.000', 2671065)

,('2013-02-01 08:02:37.000', 2671064)

,('2013-02-01 08:07:04.000', 2671063)

,('2013-02-01 08:11:09.000', 2671062)

,('2013-02-01 08:22:12.000', 2671061)

,('2013-02-01 08:22:48.000', 2671060)

Declare @StartDate Datetime = '01-Feb-2013 00:00:00.000'

Declare @endDate Datetime = '02-Feb-2013 00:00:00.000'

;with CTE

AS

(

Select

Row_NUMBER() OVER (ORDER BY object_id) Rn

from sys.all_columns

)

,Cte_Interval AS

(

Select

DateAdd(minute,(rn-1)*30,@StartDate) StartTime

, DateAdd(minute,(rn)*30,@StartDate) EndTime

from CTE

Where DateAdd(minute,(rn)*30,@StartDate)<=@EndDate

)

Select StartTime,EndTime,count(histId)

from Cte_Interval inter

LEFT JOIN #Hist hist on hist.CallDateTime >=inter.StartTime

and hist.CallDateTime<inter.EndTime

group by StartTime,EndTime

order by StartTime