SQL Server の 2 つの日付の間の週末の日数を計算できますか?

これは動作するはずです:

DECLARE @StartDate DATETIME
DECLARE @EndDate DATETIME
SET @StartDate = '2012/11/01'
SET @EndDate = '2012/11/05'


SELECT
  (DATEDIFF(wk, @StartDate, @EndDate) * 2)
   +(CASE WHEN DATENAME(dw, @StartDate) = 'Sunday'   THEN 1 ELSE 0 END)
   +(CASE WHEN DATENAME(dw, @EndDate)   = 'Saturday' THEN 1 ELSE 0 END)

http://sqlfiddle.com/#!3/d41d8/5707/0