SQL Count Data 1/2 hourly - asp.net

Question

I have a stored procedure that counts data for each hour,
Declare #DateTimeToFilter DATETIME;
--set #DateTimeToFilter = GetDate();
set #DateTimeToFilter = '6/5/14'
SET NOCOUNT ON;
WITH H ([Hour]) AS
( SELECT 7 UNION
SELECT 8 UNION
SELECT 9 UNION
SELECT 10 UNION
SELECT 11 UNION
SELECT 12 UNION
SELECT 13 UNION
SELECT 14 UNION
SELECT 15 UNION
SELECT 16 UNION
SELECT 17 UNION
SELECT 18 UNION
SELECT 19
)
SELECT H.[Hour],
COUNT(T.BookingID) AS NoOfUsers
FROM H
LEFT JOIN tbl_Visitor T
ON H.[Hour] = DATEPART(HOUR, T.TimeofArrival) AND
((DATEDIFF(dd, T.TimeofArrival, #DateTimeToFilter) = 0) AND (DATEDIFF(mm, T.TimeofArrival, #DateTimeToFilter) = 0) AND
(DATEDIFF(yy, T.TimeofArrival, #DateTimeToFilter) = 0))
GROUP BY H.[Hour];
This forces the data returned for each hour irrespective of whether there is any data or not.
How could I add the half hourly data to be added also, so the returned data look like.
Hour Count
7 0
7.5 0
8 0
8.5 0
9 0
9.5 0
10 4
10.5 0
11 0
11.5 0
12 0
12.5 0
13 0
13.5 0
14 5
14.5 0
15 2
15.5 0
16 2
16.5 0
17 0
17.5 0
18 0
18.5 0
19 0
19.5 0
The data is stored in the database as a smalltimedate, i.e. 2014-06-05 14:00:00
Any help is appreciated.

Answer 1

You can use minutes instead of hours:
with h ([Minute]) as (
select 420 union all
select 450 union all
select 480 union all
select 510 union all
select 540 union all
...
Divide the minutes to get fractional hours:
select h.[Minute] / 60.0 as [Hour], ...
Calculate the start and stop time for the interval to filter the data:
... on T.TimeofArrival >= dateadd(minute, h.[Minute], #DateTimeToFilter) and
T.TimeofArrival < dateadd(minute, h.[Minute] + 30, #DateTimeToFilter)

Answer 2

Below is an example that groups by half-hour intervals and can easily be extended for other intervals. I suggest you avoid applying functions to columns in the WHERE clause as that prevents indexes on those columns from being used efficiently.
DECLARE
#DateTimeToFilter smalldatetime = '2014-06-05'
, #IntervalStartTime time = '07:00:00'
, #IntervalEndTime time = '20:00:00'
, #IntervalMinutes int = 30;
WITH
t4 AS (SELECT n FROM (VALUES(0),(0),(0),(0)) t(n))
, t256 AS (SELECT 0 AS n FROM t4 AS a CROSS JOIN t4 AS b CROSS JOIN t4 AS c CROSS JOIN t4 AS d)
, t64k AS (SELECT ROW_NUMBER() OVER (ORDER BY (a.n)) AS num FROM t256 AS a CROSS JOIN t256 AS b)
, intervals AS (SELECT DATEADD(minute, (num - 1) * #IntervalMinutes, #DateTimeToFilter) AS interval
FROM t64k
WHERE num <= 1440 / #IntervalMinutes)
SELECT
interval
, CAST(DATEDIFF(minute, #DateTimeToFilter, interval) / 60.0 AS decimal(3, 1)) AS Hour
, COUNT(T.BookingID) AS NoOfUsers
FROM intervals
LEFT JOIN dbo.tbl_Visitor T
ON T.TimeofArrival >= intervals.interval
AND T.TimeofArrival < DATEADD(minute, #IntervalMinutes, intervals.interval)
WHERE
interval >= DATEADD(minute, DATEDIFF(minute, '', #IntervalStartTime), #DateTimeToFilter)
AND interval < DATEADD(minute, DATEDIFF(minute, '', #IntervalEndTime), #DateTimeToFilter)
GROUP BY interval
ORDER BY Hour;