Функция определения недели

USE [oktell]
GO
/****** Object:  UserDefinedFunction [dbo].[GetTimeFromSecond]    Script Date: 07.08.2019 9:32:01 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

-- =============================================
-- Author:      <Author,,Name>
-- Create date: <Create Date, ,>
-- Description: <Description, ,>
-- =============================================

ALTER FUNCTION dbo.DEV_VW_WeekSerial
    (@YearNum char(4),
    @WeekNum int)
    RETURNS NVARCHAR(51) AS

    BEGIN

        DECLARE @StartOfWeek NVARCHAR(25) = (SELECT DATEADD(wk, DATEDIFF(wk, 6, '1/1/' + @YearNum) + (@WeekNum-1), 6))

        DECLARE @EndOfWeek NVARCHAR(25) = (SELECT DATEADD(wk, DATEDIFF(wk, 5, '1/1/' + @YearNum) + (@WeekNum-1), 5))

        RETURN @StartOfWeek + '-' + @EndOfWeek

    END