T-SQL how to get date range for 2 week pay period

Question

I have following seed input data:

1. Payperiod start: Dec 3rd
2. Payperiod end: Dec 16

Thats just example how company payroll goes.

Now,

Answer 1

You need some modulo operations and DATEDIFF.

declare @periodStart datetime
declare @periodEnd datetime

set @periodStart = CAST('2011-12-03' as datetime)
set @periodEnd = CAST('2011-12-16' as datetime)

declare @anyDate datetime
set @anyDate = CAST('2011-12-30' as datetime)

declare @periodLength int
set @periodLength = DATEDIFF(day, @periodStart, @periodEnd) + 1


declare @daysFromFirstPeriod int
set @daysFromFirstPeriod = DATEDIFF(day, @periodStart, @anyDate)
declare @daysIntoPeriod int
set @daysIntoPeriod = @daysFromFirstPeriod % @periodLength

select @periodLength as periodLength, @daysFromFirstPeriod as daysFromFirstPeriod, @daysIntoPeriod as daysIntoPeriod
select DATEADD(day, -@daysIntoPeriod, @anyDate) as currentPeriodStart, DATEADD(day, @periodLength -@daysIntoPeriod, @anyDate) as currentPeriodEnd

Gives output

periodLength    daysFromFirstPeriod daysIntoPeriod
14              27                  13

and

currentPeriodStart        currentPeriodEnd
2011-12-17 00:00:00.000   2011-12-31 00:00:00.000