SQL splitting time when over midnight - sql

Question

I am after some guidance on the best way to get useful information out of our MIS database
Scenario:- I want to check staff utilisation by a variable period that I can drill down into. This needs to then be split into days so I can assess over a 24 hour period what was done
The table is huge and has loads of columns we need to calculate, so ideally I need to split the records that span 2 days into 2
The table has a datetimeformat field that has user [starttime], it then has a separate field that has [duration] which is in decimal hours.
So an example would be:
ID StartTime Duration Qty username
1 2016-11-24 23:00:00 2.00 1000 Joe Bloggs
In the example above Joe starts at 11pm and works till 1 am, so what I need is to somehow split this record in my query to put anything before midnight as 1 record and anything after into another This example is pretty simple as it is half/half but some might start at 10pm and finish at 6pm so I would need 2 hours and 6 hours.
Not sure on the best way to do this, my initial thoughts was to create a cte where a start time is in 1 day and if the starttime + duration was in the next day then split the record.
Not sure if there is an easier way or if anyone has had to do this before.
Any help appreciated

Answer 1

#Joe has the right idea, here is pseudo-SQL
SELECT ID,StartTime,Duration,Qty,username
WHERE TRUNCATE(StartTime,DAY) = TRUNCATE(StartTime + Duration hours ,DAY)
UNION
SELECT ID,StartTime, TRUNCATE(StartTime,DAY) + 1 days - StartTime hours ,Qty,username
WHERE TRUNCATE(StartTime,DAY) < TRUNCATE(StartTime+Duration hours,DAY)
UNION
SELECT ID,TRUNCATE(StartTime+Duration hour,DAY),StartTime + duration hours - DATE(StartTime+Duration),Qty,username
WHERE TRUNCATE(StartTime,DAY) < TRUNCATE(StartTime+Duration hours,DAY)
Where TRUNCATE(timestamp,DAY) truncates a timestamp to YYYY-MM-DD 00:00:00

Answer 2

You can multiply rows with join. Make Tally table, simple table with numbers 1, 2, 3... and do a join. I will use table starting at zero here:
CREATE TABLE Tally0 (Number INT IDENTITY(0,1) PRIMARY KEY NOT NULL);
GO
INSERT INTO Tally0 DEFAULT VALUES;
GO 10000
Now the harders part is conversion between dates and numerics:
;WITH
tmp1 AS (SELECT *,
DATEDIFF(SECOND, CONVERT(DATE, StartTime), StartTime)/3600.0
+ DATEPART(NANOSECOND, StartTime)/(3600*1000000000.0) AS startingHours
FROM Record),
tmp2 AS (SELECT *,
startingHours + Duration AS endingHours,
(startingHours + Duration)/24.0 AS endingDays
FROM tmp1)
SELECT *,
CASE WHEN Number = 0 THEN StartTime
ELSE DATEADD(DAY, Number, CONVERT(DATE, StartTime))
END AS StartTime2,
CASE WHEN Number = 0 AND 1 < endingDays THEN 24 - startingHours
WHEN Number = 0 THEN Duration
WHEN Number + 1 < endingDays THEN 24
ELSE endingHours - Number * 24
END AS Duration2
FROM tmp2
JOIN Tally0 ON Number < endingDays