How to count the records per half hour from a period (datetimefrom and datetimeto) field? - sql

Question

I have a table which looks like you can see below:
Id Date ScheduledTimeFrom ScheduledTimeTo ActualTimeFrom ActualTimeTo
1 2013-01-01 1899-12-30 07:00:00 1899-12-30 18:00:00 1899-12-30 07:23:00 1899-12-30 17:15:00
I need to calculate per half hour how many records exists, the output should be like:
Time Actual Count:
7:00 4
7:30 4
8:00 4
8:30 4
9:00 4
9:30 5
10:00 5
10:30 6
11:00 7
11:30 8
12:00 8
12:30 8
13:00 8
13:30 8
14:00 8
14:30 8
15:00 7
15:30 7
16:00 7
16:30 6
17:00 5
17:30 4
18:00 4
I already tried to make a helper table which should hold the times per halfhour. I have joined this helpertable with the table that contains the data and after that I tried to use a group by function but it was not working.
My query was like:
Create table period (timefrom datetime, timeto datetime)
insert into period
select '1899-12-30 07:00:00.000', '1899-12-30 07:30:00.000'
Union all
select '1899-12-30 07:30:00.000', '1899-12-30 08:00:00.000'
select *
from period p left join table1 t on t.ActualTimeFrom < p.timeto and t.ActualTimeTo >=p.timefrom
Grouping this give me no desired result....
Anyone an idea how to come to the result?
P.s. I am using sql server 2005.

Answer 1

After snooping around and testing it on my side, looks like this date function could be the answer:
DATEADD(mi,DATEDIFF(mi,0,YOUR_DATE_COLUMN)/30*30,0)