Calculate hourly average of values in a time interval - sql

Question

I'm not really a sql guy, so maybe what I'm trying to do is simple, but I can't find an easy solution.
I have a series of hourly data, between two dates. Something like this:
DATETIME VALUE
-------------------------
2014-01-01 01:00 104
2014-01-01 02:00 56
...
2014-01-04 23:00 65
2014-01-05 00:00 145
What I want is, for each hour, getting the average of the values of each day at that hour, so I end the query with something like this:
01:00 67.65
02:00 43.00
....
00:00 89.45
The "01:00" value will be the average of all the "01:00" values of each day, and so on.
The algorithm is easy, but my SQL skills are quite weak :-)
BONUS
It would be awesome if the answer would include a variation of the same problem: calculating the averages by weekdays and hour, and not only by hour:
Monday 01:00 34.23
Monday 02:00 54.34
...
Monday 23:00 241.34
Tuesday 00:00 89.43
....
Sunday 23:00 49.33

Answer 1

You can use datename , datepart and group by
select datename(weekday, [datetime]) as [Day],
datepart(hour, [datetime]) as [Hour],
avg(value) as AvgValue,
datepart(weekday, [datetime]) as [DayNo]
from table1
group by datename(weekday, [datetime]), datepart(weekday, [datetime]),
datepart(hour, [datetime])
order by datepart(weekday, [datetime]), datepart(hour, [datetime])

Answer 2

Below is an example of a general aggregate query you can use to group by a time interval.
WITH intervals AS (
SELECT DATEADD(hour, DATEDIFF(hour, '', DATETIME), '') AS TimeInterval
,VALUE
FROM dbo.Foo
)
SELECT
TimeInterval
, DATENAME(weekday, TimeInterval) AS Weekday
, CAST(TimeInterval AS time)
, AVG(VALUE) AS AvgValue
FROM intervals
GROUP BY TimeInterval
ORDER BY TimeInterval;