Get last Friday's Date unless today is Friday using T-SQL

Question

I'm trying to get the correct SQL code to obtain last Friday's date. A few days ago, I thought I had my code correct. But just noticed that it's getting last week's Friday date, not the last Friday. The day I'm writing this question is Saturday, 8/11/2012 @ 12:23am. In SQL Server, this code is returning Friday, 8/3/2012. However, I want this to return Friday, 8/10/2012 instead. How can I fix this code? Since we're getting to specifics here, if the current day is Friday, then I want to return today's date. So if it were yesterday (8/10/2012) and I ran this code yesterday, then I would want this code to return 8/10/2012, not 8/3/2012.

SELECT DATEADD(DAY, -3, DATEADD(WEEK, DATEDIFF(WEEK, 0, GETDATE()), 0))

Answer 1

try this:

declare @date datetime;
set @date='2012-08-09'
SELECT case when datepart(weekday, @date) >5 then
 DATEADD(DAY, +4, DATEADD(WEEK, DATEDIFF(WEEK, 0, @date), 0)) 
else DATEADD(DAY, -3, DATEADD(WEEK, DATEDIFF(WEEK, 0, @date), 0)) end

result:

2012-08-03 

Example2:

declare @date datetime;
set @date='2012-08-10'
SELECT case when datepart(weekday, @date) >5 then
 DATEADD(DAY, +4, DATEADD(WEEK, DATEDIFF(WEEK, 0, @date), 0)) 
else DATEADD(DAY, -3, DATEADD(WEEK, DATEDIFF(WEEK, 0, @date), 0)) end

result:

  2012-08-10 

Answer 2

Modular arithmetic is the most direct approach, and order of operations decides how Fridays are treated:

DECLARE @test_date DATETIME = '2012-09-28'

SELECT DATEADD(d,-1-(DATEPART(dw,@test_date) % 7),@test_date) AS Last_Friday
      ,DATEADD(d,-(DATEPART(dw,@test_date+1) % 7),@test_date) AS This_Friday