How to split the time range into multiple rows - sql

Question

I want to split the date/time ranges into multiple rows by hour in SQL Server but have some issues. My current dataset looks like this:
EmployeeCode StartDateTime EndDateTime
843578 2017-05-14 8:30 AM 2017-05-14 11:36 PM
587123 2017-05-14 22:00 PM 2017-05-15 01:28 AM
And I want something like this as my result table. Note that I want to treat a block less than an hour as one independent row as well. (For example 8:30AM - 9:00AM as one row.)
EmployeeCode StartDateTime EndDateTime
843578 2017-05-14 8:30 AM 2017-05-14 9:00 PM
843578 2017-05-14 9:00 AM 2017-05-14 10:00 AM
843578 2017-05-14 10:00 AM 2017-05-14 11:00 AM
843578 2017-05-14 11:00 AM 2017-05-14 11:36 AM
587123 2017-05-14 22:00 PM 2017-05-14 23:00 PM
587123 2017-05-14 23:00 PM 2017-05-15 00:00 AM
587123 2017-05-15 00:00 AM 2017-05-15 01:00 AM
587123 2017-05-15 01:00 AM 2017-05-15 01:28 AM
My current code only splits the date/time range that is within the same day. For example, the time range for Employee 587123 stops the spliting at 22:00 - 23:00 and doesn't work for the time range in next day.
How do I update my code to capture data after midnight? (The last three rows in the sample result table.)
Here's my current code
SELECT YT.EmployeeCode,
CASE WHEN YT.StartDateTime > DT.StartDateTime THEN YT.StartDateTime ELSE DT.StartDateTime END AS StartDateTime,
CASE WHEN YT.EndDateTime < DT.EndDateTime THEN YT.EndDateTime ELSE DT.EndDateTime END AS StartDateTime
FROM (VALUES(843578,CONVERT(datetime2(0),'2017-05-14T08:30:00'),CONVERT(datetime2(0),'2017-05-14T15:36:00')),
(587123,CONVERT(datetime2(0),'2017-05-14T09:00:00'),CONVERT(datetime2(0),'2017-05-14T18:28:00')))YT(EmployeeCode,StartDateTime,EndDateTime)
CROSS APPLY (VALUES(0),(1),(2),(3),(4),(5),(6),(7),(8),(9),(10),(11),(12),(13),(14),(15),(16),(17),(18),(19),(20),(21),(22),(23))T(I)
CROSS APPLY (VALUES(DATEADD(HOUR,T.I,CONVERT(time(0),'00:00:00')),DATEADD(HOUR,T.I+1,CONVERT(time(0),'00:00:00'))))V(StartTime,EndTime)
CROSS APPLY (VALUES(DATETIMEFROMPARTS(YEAR(YT.StartDateTime),MONTH(YT.StartDateTime),DAY(YT.StartDateTime),DATEPART(HOUR,V.StartTime),DATEPART(MINUTE,V.StartTime),0,0),
DATETIMEFROMPARTS(YEAR(YT.StartDateTime),MONTH(YT.StartDateTime),DAY(YT.StartDateTime),DATEPART(HOUR,V.EndTime),DATEPART(MINUTE,V.EndTime),0,0)))DT(StartDateTime,EndDateTime)
WHERE YT.StartDateTime <= DT.EndDateTime
AND YT.EndDateTime >= DT.StartDateTime;
The current code looks too complicated so if you know better way to do this, please let me know.
I'd appreciate any help on this.

Answer 1

Here is a recursive CTE solution:
with cte as (
select
employeecode,
startdatetime,
dateadd(hour, 1, datetimefromparts(year(startdatetime), month(startdatetime), day(startdatetime), datepart(hour, startdatetime), 0, 0, 0)) enddatetime
enddatetime maxdatetime
from mytable
union all
select employeecode, enddatetime, dateadd(hour, 1, enddatetime), maxdatetime
from cte
where enddatetime < maxdatetime
)
select employeecode, startdatetime,
case when enddatetime < maxdatetime then enddatetime else maxdatetime end as enddatetime
from cte
Basically, the anchor of the CTE performs computes the end of the first range, using datetimefrompart(). Then we iteratively generate the following ranges, until the maximum date time is reached. We can then display the results with the outer query, while adjusting the end date of the last range.

Answer 2

I would approach this using a recursive CTE:
with cte as (
select t.EmployeeCode, t.StartDateTime as startdt,
dateadd(hour, datepart(hour, t.startdatetime) + 1, convert(datetime, convert(date, t.StartDateTime))) as enddt,
t.endDateTime, 1 as lev
from t
union all
select cte.employeecode, enddt,
(case when dateadd(hour, 1, enddt) < enddatetime then dateadd(hour, 1, enddt) else enddatetime end),
enddatetime, lev + 1
from cte
where enddt < enddatetime
)
select *
from cte
order by employeecode, startdt;
Here is a db<>fiddle.
If you might have spans of more than 100 hours, then you need option (maxrecursion 0) for the query.