SQL Server-月的总小时数

Question

I have the case when i need to calculate the total contracted hours of an employee in a given 4 week period. The employee may change hours mid period and hence the total contracted hours would need to adjust based on when the hours changed

My SQL is

declare @start datetime = '2017-06-20'
declare @end datetime = '2017-07-20'

select j.EMPLOY_REF, 
j.ACT_HOURS * 4 as ContractedHoursPer4WeekPeriod, 
j.ACT_HOURS as ContractedHoursPerWeek, 
(j.ACT_HOURS / 7) as ContractedHoursPerDay,
j.COSTCENTRE, 
j.FROMDATE, 
j.UNTILDATE 

from jobholdr j

where EMPLOY_REF ='000033504'

and the result being

If the period ran in this example from 20th June 2017 until 20 July 2017 then they should have 10 days at 39 hours per week and then 20 days at 30 hours per week.

How can this be calculated to give one result for total contracted hours in the period given the difference of contracted hours over the period. I am guessing it needs to be done by breaking it down into days but I am not sure where to go next...

Answer 1

You can include in your SELECT the following

DATEDIFF(day, CASE WHEN @start > j.fromdate 
                   THEN @start 
                   WHEN @start = j.fromdate 
                   THEN j.fromdate 
                   ELSE DATEADD(day,-1,j.fromdate)
               END, 
              CASE WHEN @end > j.untildate 
                   THEN j.untildate 
                   ELSE @end
               END) * (j.act_hours / 7) TotalContractedHours,