How do I count overlapping vacation days? - sql

Question

I have a Timesheet table in SQL Server which stores personnel roles
CREATE TABLE [dbo].[TimeSheetTable](
[pk_TimeSheetID] [bigint] IDENTITY(1,1) NOT NULL,
[fk_PersonelID] [int] NOT NULL,
[StartDate] [datetime] NOT NULL,
[EndDate] [datetime] NOT NULL,
[fk_RoleID] [int] NOT NULL,
[Comments] [nvarchar](2000) NULL,
[dateCreated] [datetime] NOT NULL,
[CreatedBy] [int] NULL,
Sometimes, an employee can take a vacation, with overlapping months, starting from 28-Oct-2012 to 2-Nov-2012. With the above example, the employee had 4 days in October and 3 days in November.
My problem is writing a query that counts the number of days of vacation taken for each. If the enddate exceeds the month, it shouldn't count that.
SELECT TOP 1000
sum(DATEDIFF(day,startdate,EndDate))
FROM [db_ASCO_Personel].[dbo].[TimeSheetTable]
where fk_RoleID=51 /* how do I count leave days that over lap between two months*/
Row #17 has a 1 day in nov and 2days in dec( total 3 days vacation). how do I count the number of vacation days taking by each employee for 1 month alone?
TimeSheetID StartDate EndDate RoleID Comments dateCreated CreatedBy
15 August-6-2012 August-7-2012 51 03:10.6 NULL
16 August-1-2012 August-2-2012 51 03:31.5 NULL
17 November-29-2012 December-3-2012 51 51:15.5 NULL

Answer 1

You need to know the start and end of the month. Something like this:
with const as (
select cast('2012-09-01' as date) as MonthStart, cast('2012-09-30' as date) as MonthEnd
)
select sum(DATEDIFF(day,
(case when startdate < const.MonthStart then const.MonthStart else startdate end),
(case when enddate > const.MonthEnd then const.MontEnd else ndDate end)
)
FROM [db_ASCO_Personel].[dbo].[TimeSheetTable] tst cross join
const
where fk_RoleID=51 and
startdate <= const.MonthEnd and
enddate >= const.MonthStart

Answer 2

I would just grab the data and calculate with c# and put into a new table (or do whatever needs to be done with the values)
but if you can be sure that vacation time will never be more than an entire month (ex start is jan and end is never later than feb) then you could do some if else
SELECT TOP 1000 CASE
WHEN month(startDate) = month(enddate)
THEN sum(DATEDIFF(day,startdate,EndDate)) as daymonth1, 0 as daysmonth2
ELSE sum(DATEDIFF(day,startdate,EndDate)) - day(enddate) as daymonth1,day(enddate) as daysmonth2
END
FROM [db_ASCO_Personel].[dbo].[TimeSheetTable]
where fk_RoleID=51
check that syntax as I dont have ssms on this comp to fully test
Edit: to powaga: Unless I'm stupid he did (just not clearly) he said he wants to return 4 and 3 instead of 7 ... he want the resulting number of days to be per month instead of number of days