GROUP BY several hours - sql

Question

I have a table where our product records its activity log. The product starts working at 23:00 every day and usually works one or two hours. This means that once a batch started at 23:00, it finishes about 1:00am next day.
Now, I need to take statistics on how many posts are registered per batch but cannot figure out a script that would allow me achiving this. So far I have following SQL code:
SELECT COUNT(*), DATEPART(DAY,registrationtime),DATEPART(HOUR,registrationtime)
FROM RegistrationMessageLogEntry
WHERE registrationtime > '2014-09-01 20:00'
GROUP BY DATEPART(DAY, registrationtime), DATEPART(HOUR,registrationtime)
ORDER BY DATEPART(DAY, registrationtime), DATEPART(HOUR,registrationtime)
which results in following
count day hour
....
1189 9 23
8611 10 0
2754 10 23
6462 11 0
1885 11 23
I.e. I want the number for 9th 23:00 grouped with the number for 10th 00:00, 10th 23:00 with 11th 00:00 and so on. How could I do it?

Answer 1

You can do it very easily. Use DATEADD to add an hour to the original registrationtime. If you do so, all the registrationtimes will be moved to the same day, and you can simply group by the day part.
You could also do it in a more complicated way using CASE WHEN, but it's overkill on the view of this easy solution.

Answer 2

I had to do something similar a few days ago. I had fixed timespans for work shifts to group by where one of them could start on one day at 10pm and end the next morning at 6am.
What I did was:
Define a "shift date", which was simply the day with zero timestamp when the shift started for every entry in the table. I was able to do so by checking whether the timestamp of the entry was between 0am and 6am. In that case I took only the date of this DATEADD(dd, -1, entryDate), which returned the previous day for all entries between 0am and 6am.
I also added an ID for the shift. 0 for the first one (6am to 2pm), 1 for the second one (2pm to 10pm) and 3 for the last one (10pm to 6am).
I was then able to group over the shift date and shift IDs.
Example:
Consider the following source entries:
Timestamp SomeData
=============================
2014-09-01 06:01:00 5
2014-09-01 14:01:00 6
2014-09-02 02:00:00 7
Step one extended the table as follows:
Timestamp SomeData ShiftDay
====================================================
2014-09-01 06:01:00 5 2014-09-01 00:00:00
2014-09-01 14:01:00 6 2014-09-01 00:00:00
2014-09-02 02:00:00 7 2014-09-01 00:00:00
Step two extended the table as follows:
Timestamp SomeData ShiftDay ShiftID
==============================================================
2014-09-01 06:01:00 5 2014-09-01 00:00:00 0
2014-09-01 14:01:00 6 2014-09-01 00:00:00 1
2014-09-02 02:00:00 7 2014-09-01 00:00:00 2

Answer 3

If you add one hour to registrationtime, you will be able to group by the date part:
GROUP BY
CAST(DATEADD(HOUR, 1, registrationtime) AS date)
If the starting hour must be reflected accurately in the output (as 9, 23, 10, 23 rather than as 10, 0, 11, 0), you could obtain it as MIN(registrationtime) in the SELECT clause:
SELECT
count = COUNT(*),
day = DATEPART(DAY, MIN(registrationtime)),
hour = DATEPART(HOUR, MIN(registrationtime))
Finally, in case you are not aware, you can reference columns by their aliases in ORDER BY:
ORDER BY
day,
hour
just so that you do not have to repeat the expressions.

Answer 4

The below query will give you what you are expecting..
;WITH CTE AS
(
SELECT COUNT(*) Count, DATEPART(DAY,registrationtime) Day,DATEPART(HOUR,registrationtime) Hour,
RANK() over (partition by DATEPART(HOUR,registrationtime) order by DATEPART(DAY,registrationtime),DATEPART(HOUR,registrationtime)) Batch_ID
FROM RegistrationMessageLogEntry
WHERE registrationtime > '2014-09-01 20:00'
GROUP BY DATEPART(DAY, registrationtime), DATEPART(HOUR,registrationtime)
)
SELECT SUM(COUNT) Count,Batch_ID
FROM CTE
GROUP BY Batch_ID
ORDER BY Batch_ID

Answer 5

You can write a CASE statement as below
CASE WHEN DATEPART(HOUR,registrationtime) = 23
THEN DATEPART(DAY,registrationtime)+1
END,
CASE WHEN DATEPART(HOUR,registrationtime) = 23
THEN 0
END