SET ANSI_NULLS OFF
GO
SET QUOTED_IDENTIFIER ON
GO

CREATE FUNCTION Week  (@FLTDATE float)
RETURNS int
AS
BEGIN
  DECLARE @DATE datetime
  DECLARE @Week int
   SET @DATE = DATEADD(s,@FLTDATE,'1980')
   SET @Week= DATEPART(wk,@DATE)+1
      -DATEPART(wk,CAST(DATEPART(yy,@DATE) as CHAR(4))+'0104')
--Special cases: Jan 1-3 may belong to the previous year
   IF (@Week=0) 
      SET @Week=dbo.Week(DATEDIFF(s,'1980',CAST(DATEPART(yy,@DATE)-1 
         AS CHAR(4))+'12'+ CAST(24+DATEPART(DAY,@DATE) AS CHAR(2))))+1
--Special case: Dec 29-31 may belong to the next year
   IF ((DATEPART(mm,@DATE)=12) AND 
      ((DATEPART(dd,@DATE)-DATEPART(dw,@DATE))>= 28))
      SET @Week=1
   RETURN(@Week)
END

GO