Get the most recent Friday's date SQL

Question

I\'m trying to get the most recent Friday in SQL Server 2008.

I have this. It gets the beginning of the week (monday) then subtracts 3 days to get Friday.

Answer 1

Using a known Friday date (I'll use Jan 7, 2011) as a starting point, you can do this:

DECLARE @d DATETIME

SET @d = '2011-05-13' /* Friday */
SELECT DATEADD(DAY, (DATEDIFF (DAY, '20110107', @d) / 7) * 7, '20110107')
/* Returns 2011-05-13 */

SET @d = '2011-05-12' /* Thursday */
SELECT DATEADD(DAY, (DATEDIFF (DAY, '20110107', @d) / 7) * 7, '20110107')
/* Returns 2011-05-06 */

Just choose a known Friday that's older than any dates you'll be using in your calculations.

Answer 2

This works for any input and any setting of DATEFIRST:

dateadd(d, -((datepart(weekday, getdate()) + 1 + @@DATEFIRST) % 7), getdate())

It works by adjusting the weekday value so that 0 = Friday, simulating Friday as the beginning of the week. Then subtract the weekday value if non-zero to get the most recent Friday.

Edit: Updated to work for any setting of DATEFIRST.