Calculate the last day of the quarter

Question

What's the most efficient way to calculate the last day of the prior quarter?

Example: given the date 11/19/2008, I want to return 9/30/2008.

Platform is SQL Server

Answer 1

I came up with this (tested for all months):

select dateadd(dd,-1,dateadd(qq,datediff(qq,0,'11/19/2008'),0)),
       dateadd(dd,-1,dateadd(qq,datediff(qq,0,'10/19/2008'),0)),
       dateadd(dd,-1,dateadd(qq,datediff(qq,0,'12/19/2008'),0))

It might turn out to be the simplest.

Answer 2

If @Date has the date in question

Select DateAdd(day, -1, dateadd(qq, DateDiff(qq, 0, @Date), 0))

Answer 3

actually simpler is: SELECT DATEADD(qq, DATEDIFF(qq,0,getdate()), -1)