How to calcute future datetime after few workinghours - sql

Question

I am trying to calculate what date will be after 2 or more working hours from now even if I'll start calculating on weekend or after workhours it should be like:
working hours are from 8am to 4pm
I start calculating at Friday at 3pm so if I'll start calculating result should be Monday 9am
if(#data_przyj>#WorkStart AND DATEPART(DATEADD(MINUTE,#ileNaZapytanie,#data_przyj)<#WorkFinish)
BEGIN
while (DATEPART(dw, #CurrentDate)!=1 AND DATEPART(dw, #CurrentDate)!=7))
BEGIN
SET #CurrentDate = DATEADD(day, 1, #CurrentDate)
SET #czyBylPrzeskok =1
END
if (#czyBylPrzeskok =1)
BEGIN
SET #LastDay = #CurrentDate
SET #LastDay = DATEADD(MINUTE, datediff(MINUTE,DATEADD(dd, 0, DATEDIFF(MINUTE, 0, #data_przyj)),#WorkStart), #LastDay)
SET #LastDay = DATEADD(HOUR, datediff(MINUTE,DATEADD(dd, 0, DATEDIFF(HOUR, 0, #data_przyj)),#WorkStart), #LastDay)
END
ELSE
BEGIN
SET #LastDay = DATEADD(MINUTE,#ileNaZapytanie,#data_przyj)
END
SET #IsCalculated = 1
END
else if(#data_przyj>#WorkStart AND DATEADD(MINUTE,#ileNaZapytanie,#data_przyj)>#WorkFinish)
BEGIN
SET #LastDay =DateADD(DD,3,GETDATE());
SET #IsCalculated = 1
END
else if(#data_przyj<#WorkStart )
BEGIN
SET #LastDay =GETDATE();
SET #IsCalculated = 1
END
END
EDIT:
for example working hours:8:00 - 16:00 i have Date '2019-09-06 15:00' so after adding 2 working hours should be '2019-09-09 09:00', for date '2019-09-06 13:00' should be '2019-09-06 15:00' etc

Answer 1

The following solution uses a calendar table with working hours, then use a rolling sum to accumulate each day's business hours and find which day you need to end with.
Using a calendar table will give you the flexibility of having different business time periods and very easily adding or removing holidays.
Setup (calendar table):
IF OBJECT_ID('tempdb..#WorkingCalendar') IS NOT NULL
DROP TABLE #WorkingCalendar
CREATE TABLE #WorkingCalendar (
Date DATE PRIMARY KEY,
IsWorkingDay BIT,
WorkingStartTime DATETIME,
WorkingEndTime DATETIME)
SET DATEFIRST 1 -- 1: Monday, 7: Sunday
DECLARE #StartDate DATE = '2019-01-01'
DECLARE #EndDate DATE = '2030-01-01'
;WITH RecursiveDates AS
(
SELECT
GeneratedDate = #StartDate
UNION ALL
SELECT
GeneratedDate = DATEADD(DAY, 1, R.GeneratedDate)
FROM
RecursiveDates AS R
WHERE
R.GeneratedDate < #EndDate
)
INSERT INTO #WorkingCalendar (
Date,
IsWorkingDay,
WorkingStartTime,
WorkingEndTime)
SELECT
Date = R.GeneratedDate,
IsWorkingDay = CASE
WHEN DATEPART(WEEKDAY, R.GeneratedDate) BETWEEN 1 AND 5 THEN 1 -- From Monday to Friday
ELSE 0 END,
WorkingStartTime = CASE
WHEN DATEPART(WEEKDAY, R.GeneratedDate) BETWEEN 1 AND 5
THEN CONVERT(DATETIME, R.GeneratedDate) + CONVERT(DATETIME, '08:00:00') END,
WorkingEndTime = CASE
WHEN DATEPART(WEEKDAY, R.GeneratedDate) BETWEEN 1 AND 5
THEN CONVERT(DATETIME, R.GeneratedDate) + CONVERT(DATETIME, '16:00:00') END
FROM
RecursiveDates AS R
OPTION
(MAXRECURSION 0)
Generates a table like the following:
+------------+--------------+-------------------------+-------------------------+
| Date | IsWorkingDay | WorkingStartTime | WorkingEndTime |
+------------+--------------+-------------------------+-------------------------+
| 2019-01-01 | 1 | 2019-01-01 08:00:00.000 | 2019-01-01 16:00:00.000 |
| 2019-01-02 | 1 | 2019-01-02 08:00:00.000 | 2019-01-02 16:00:00.000 |
| 2019-01-03 | 1 | 2019-01-03 08:00:00.000 | 2019-01-03 16:00:00.000 |
| 2019-01-04 | 1 | 2019-01-04 08:00:00.000 | 2019-01-04 16:00:00.000 |
| 2019-01-05 | 0 | NULL | NULL |
| 2019-01-06 | 0 | NULL | NULL |
| 2019-01-07 | 1 | 2019-01-07 08:00:00.000 | 2019-01-07 16:00:00.000 |
| 2019-01-08 | 1 | 2019-01-08 08:00:00.000 | 2019-01-08 16:00:00.000 |
| 2019-01-09 | 1 | 2019-01-09 08:00:00.000 | 2019-01-09 16:00:00.000 |
| 2019-01-10 | 1 | 2019-01-10 08:00:00.000 | 2019-01-10 16:00:00.000 |
| 2019-01-11 | 1 | 2019-01-11 08:00:00.000 | 2019-01-11 16:00:00.000 |
| 2019-01-12 | 0 | NULL | NULL |
| 2019-01-13 | 0 | NULL | NULL |
| 2019-01-14 | 1 | 2019-01-14 08:00:00.000 | 2019-01-14 16:00:00.000 |
| 2019-01-15 | 1 | 2019-01-15 08:00:00.000 | 2019-01-15 16:00:00.000 |
| 2019-01-16 | 1 | 2019-01-16 08:00:00.000 | 2019-01-16 16:00:00.000 |
| 2019-01-17 | 1 | 2019-01-17 08:00:00.000 | 2019-01-17 16:00:00.000 |
+------------+--------------+-------------------------+-------------------------+
Proposed Solution:
DECLARE #v_BusinessHoursToAdd INT = 2
DECLARE #v_CurrentDateTimeHour DATETIME = '2019-09-06 15:00'
;WITH CalendarFromNow AS
(
SELECT
T.Date,
WorkingStartTime = CASE
WHEN #v_CurrentDateTimeHour BETWEEN T.WorkingStartTime AND T.WorkingEndTime THEN #v_CurrentDateTimeHour
ELSE T.WorkingStartTime END,
WorkingEndTime = T.WorkingEndTime
FROM
#WorkingCalendar AS T
WHERE
T.Date >= CONVERT(DATE, #v_CurrentDateTimeHour) AND
T.IsWorkingDay = 1
),
RollingBusinessSum AS
(
SELECT
C.Date,
C.WorkingStartTime,
C.WorkingEndTime,
AmountBusinessHours = DATEDIFF(HOUR, C.WorkingStartTime, C.WorkingEndTime),
RollingBusinessHoursSum = SUM(DATEDIFF(HOUR, C.WorkingStartTime, C.WorkingEndTime)) OVER (ORDER BY C.Date),
PendingHours = #v_BusinessHoursToAdd - SUM(DATEDIFF(HOUR, C.WorkingStartTime, C.WorkingEndTime)) OVER (ORDER BY C.Date)
FROM
CalendarFromNow AS C
)
SELECT TOP 1
EndingHour = DATEADD(
HOUR,
R.PendingHours,
R.WorkingEndTime)
FROM
RollingBusinessSum AS R
WHERE
R.PendingHours < 0
ORDER BY
R.Date
Explanation:
The first CTE CalendarFromNow is simply filtering the calendar dates from the current hour's date and reducing the starting working datetime to the current hour, since this is gonna be the starting point to count hours from.
+------------+-------------------------+-------------------------+
| Date | WorkingStartTime | WorkingEndTime |
+------------+-------------------------+-------------------------+
| 2019-09-06 | 2019-09-06 15:00:00.000 | 2019-09-06 16:00:00.000 |
| 2019-09-09 | 2019-09-09 08:00:00.000 | 2019-09-09 16:00:00.000 |
| 2019-09-10 | 2019-09-10 08:00:00.000 | 2019-09-10 16:00:00.000 |
| 2019-09-11 | 2019-09-11 08:00:00.000 | 2019-09-11 16:00:00.000 |
| 2019-09-12 | 2019-09-12 08:00:00.000 | 2019-09-12 16:00:00.000 |
| 2019-09-13 | 2019-09-13 08:00:00.000 | 2019-09-13 16:00:00.000 |
| 2019-09-16 | 2019-09-16 08:00:00.000 | 2019-09-16 16:00:00.000 |
+------------+-------------------------+-------------------------+
The second CTE RollingBusinessSum is calculating the amount of business hours on each day and accumulating them over the days. The last column PendingHours is the result of the amount of hours we need to add from now subtracted by the sum of business hours over the days.
+------------+-------------------------+-------------------------+---------------------+-------------------------+--------------+
| Date | WorkingStartTime | WorkingEndTime | AmountBusinessHours | RollingBusinessHoursSum | PendingHours |
+------------+-------------------------+-------------------------+---------------------+-------------------------+--------------+
| 2019-09-06 | 2019-09-06 15:00:00.000 | 2019-09-06 16:00:00.000 | 1 | 1 | 1 |
| 2019-09-09 | 2019-09-09 08:00:00.000 | 2019-09-09 16:00:00.000 | 8 | 9 | -7 |
| 2019-09-10 | 2019-09-10 08:00:00.000 | 2019-09-10 16:00:00.000 | 8 | 17 | -15 |
| 2019-09-11 | 2019-09-11 08:00:00.000 | 2019-09-11 16:00:00.000 | 8 | 25 | -23 |
| 2019-09-12 | 2019-09-12 08:00:00.000 | 2019-09-12 16:00:00.000 | 8 | 33 | -31 |
| 2019-09-13 | 2019-09-13 08:00:00.000 | 2019-09-13 16:00:00.000 | 8 | 41 | -39 |
+------------+-------------------------+-------------------------+---------------------+-------------------------+--------------+
Finally the first day that the PendingHours column is negative is the day that we arrived at the amount of hours we wanted to add. This is the TOP 1 with ORDER BY. To get the final datetime, we just subtract the pending hours to the end time for that particular day.
+------------+-------------------------+-------------------------+---------------------+-------------------------+--------------+-------------------------+
| Date | WorkingStartTime | WorkingEndTime | AmountBusinessHours | RollingBusinessHoursSum | PendingHours | EndingHour |
+------------+-------------------------+-------------------------+---------------------+-------------------------+--------------+-------------------------+
| 2019-09-09 | 2019-09-09 08:00:00.000 | 2019-09-09 16:00:00.000 | 8 | 9 | -7 | 2019-09-09 09:00:00.000 |
+------------+-------------------------+-------------------------+---------------------+-------------------------+--------------+-------------------------+
You might have to tweak performance and do boundary tests but this might give you a flexible idea of how to work with working hours at holidays or different time periods.