Number of specific one-hour periods between two date/times - sql

Question

I have a table of table records, call it "game"
It has an id and timestamp.
What I need to know is unrelated to the table specifically. In order to know the average number of games played per hour, I need to know :
Total games played for each hour over the date range
Number of hourly
periods between the date range.
Finding the first is a matter of extracting the hour from the timestamp and grouping by it.
For the second, if the date range was rounded to the nearest day, finding this value would be easy (totalgames/numdays).
Unfortunately I can't assume this. What I need help with is finding the number of specific hour periods existing within a time range.
Example:
If the range is 5 PM today to 8 PM tomorrow, there is one "00" hour (midnight to 1 AM), but two 17, 18, 19 hours (5-6, 6-7, 7-8)
Thanks for the help
Edit: for clarity, consider the following query:
I have table game:
id, daytime
select EXTRACT(hour from daytime) as hour_period, count (*)
from game
where daytime > dateFrom and daytime < dayTo
group by hour_period
This will give me the number of games played broken down into hourly chunks for the time period.
In order to find the average games played per hour, I need to know exactly how many specific hour durations are between two timestamps. Simply dividing by the number of days is not accurate.
Edit: The ideal output will look something like this:
00 275
01 300
02 255
...
Consider the following: How many times does midnight occur between date 1 and date 2 ? If you have 1.5 days, that doesn't guarantee that midnight will occur twice. 6 AM today to 6 PM tomorrow night, for example, has 1 midnight, but 9PM tonight to 9 AM two days from now has 2 midnights.
What I'm trying to find is how many of the EXACT HOUR occurs between two timestamps, so I can use it to average the number of games played at THAT HOUR over a time period.

Answer 1

EDIT:
The following query gets the days, hours, and # of games, giving an output as below:
29 23 100
29 00 130
30 22 140
30 23 150
Then, the outer query adds up the number of games for each distinct hour and divides by the number of hours, as follows
22 140
23 125
00 130
The modified query is below:
SELECT
hour_period,
sum(hourly_no_of_games) / count(hour_period)
FROM
(
SELECT
EXTRACT(DAY from daytime) as day_period,
EXTRACT(HOUR from daytime) as hour_period,
count (*) hourly_no_of_games
from game
where daytime > dateFrom and daytime < dayTo
group by EXTRACT(DAY from daytime), EXTRACT(HOUR from daytime)
) hourly_data
GROUP BY hour_period
ORDER BY hour_period;
SQL Fiddle demo

Answer 2

If you need something to GROUP BY, you can truncate the timestamp to the level of hour, as in the following:
DECLARE #Date DATETIME
SET #Date = GETDATE()
SELECT #Date, DATEADD(Hour, DATEDIFF(Hour, 0, #Date), 0) AS RoundedDate
If you just need to find the total hours, you can just select the DATEDIFF in hours, such as with
SELECT DATEDIFF(Hour, '5/29/2014 20:01:32.999', GETDATE())

Answer 3

Extract not only the hour of the day but the day of the year (1-366). Then group on those. If there is the possibility the interval could span a year, then add the year itself and group by all three.
year dy hr games
2013 365 23 115
2014 1 00 103