Week Function

程序开发过程中需要做周别统计与显示报表。在做之前，得先找出所在年份周别的开始日期与结束日期。每年每周的开始与结束日期都不尽相同。为了该功能，在sql Server自定义一个用户定义星期函数。
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以下内容于20120105更新：
2012年刚到，开发的软件使用这个函数发现bug。2012年第一周应该是2012-01-01至2012-01-07，但此函数却把2012-01-08至2012-01-14当作第一周。

就此bug对此函数修改如下：

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER FUNCTION [dbo].[udf_Week]
(
    @StartYear INT,
    @EndYear INT
)
RETURNS @Week TABLE([WeekId] INT IDENTITY(1,1) PRIMARY KEY,[Year] [INT] NULL,[Week] [INT] NULL,[StartDate] [DATETIME] NULL,[EndDate] [DATETIME] NULL)
AS
BEGIN
    DECLARE @YearStartDate DATETIME 
    DECLARE @YearEndDate DATETIME 
    DECLARE @WeekStartDate DATETIME 
    DECLARE @WeekEndDate DATETIME 
    DECLARE @Weeks INT 

    WHILE @StartYear <= @EndYear
    BEGIN
        SET @YearStartDate = CAST((CAST(@StartYear AS VARCHAR(4)) + '-01-01') AS DATETIME)
        SET @YearEndDate= CAST((CAST(@StartYear AS VARCHAR(4))+ '-12-31') AS DATETIME)
        SET @Weeks = 1         
        
        IF DATEPART(DW,@YearStartDate) > 4
            SET @YearStartDate = DATEADD(DAY,(8 - DATEPART(DW,@YearStartDate)) ,@YearStartDate)
        ELSE 
            SET @YearStartDate = DATEADD(DAY,(-(DATEPART(DW,@YearStartDate)-1)),@YearStartDate)

        SET @WeekStartDate = @YearStartDate
        SET @WeekEndDate = DATEADD(DAY,6,@WeekStartDate)
        WHILE DATEDIFF(DAY,@WeekStartDate,@YearEndDate) >= 4
        BEGIN
            INSERT INTO @Week([Year],[Week],[StartDate],[EndDate]) VALUES (@StartYear,@Weeks,@WeekStartDate,@WeekEndDate)
            SET @Weeks = @Weeks + 1
            SET @WeekStartDate = @WeekStartDate + 7
            SET @WeekEndDate = @WeekEndDate + 7
        END
        SET @StartYear = @StartYear + 1
    END  
        RETURN
END

 下面内容于2014-12-29 10:45分补充：
今天程序发现这个函数有bug：

WHILE DATEDIFF(DAY,@WeekStartDate,@YearEndDate) >= 4

 
2014年最后一周是从2014-12-28至31号，它们有4天时间。因此需要加1天才是正确的：

WHILE DATEDIFF(DAY,@WeekStartDate,@YearEndDate) + 1 >= 4