在此 TSQL 存储过程中进行日期数学运算的正确方法是什么？

Question

这是我的业务案例：我需要根据用户输入的 "BegDate" 和 "EndDate" 日期值来确定另外两个日期。具体来说，我需要知道：

Week1Begin (which is the value they enter for "BegDate")
Week2End (which is the value they enter for "EndDate")
Week1End (which is the value they enter for "BegDate" + 6 days)
Week2Begin (which is the value they enter for "BegDate" + 7 days)

IOW，如果用户输入这些值：

BegDate = 12/27/2015
EndDate = 1/6/2016

...其他值需要计算为：

Week1End = 1/2/2016
Week2Begin = 1/3/2016

我有一个执行的存储过程，但 returns 求和列中的所有 Null 和 0，可能是因为日期数学尚未包含在 SP 中。这是现在的 SP：

CREATE PROCEDURE [dbo].[duckbilledPlatypi]
    @Unit varchar(25),
    @BegDate datetime,
    @EndDate datetime
AS

DECLARE 
@Week1End datetime,
@Week2Begin datetime

Select Ind.Description,
    @BegDate  BegDate,
    @Week1End Week1End,
    @Week1End Week2Begin,
    @EndDate EndDate,
    SUM(CASE WHEN Ind.InvoiceDate BETWEEN @BegDate AND @Week1End THEN Ind.QtyShipped ELSE 0 END) 
Week1Usage,
    SUM(CASE WHEN Ind.InvoiceDate BETWEEN @Week2Begin AND @EndDate THEN Ind.QtyShipped ELSE 0 END) 
Week2Usage,
    SUM(CASE WHEN Ind.InvoiceDate BETWEEN @BegDate AND @Week1End THEN Ind.Price ELSE 0 END) 
Week1Price,
    SUM(CASE WHEN Ind.InvoiceDate BETWEEN @Week2Begin AND @EndDate THEN Ind.Price ELSE 0 END) -
   SUM(CASE WHEN Ind.InvoiceDate BETWEEN @BegDate AND @Week1End THEN Ind.QtyShipped ELSE 0 END) 
UsageVariance,
    SUM(CASE WHEN Ind.InvoiceDate BETWEEN @Week2Begin AND @EndDate THEN Ind.QtyShipped ELSE 0 END) 
 -
    SUM(CASE WHEN Ind.InvoiceDate BETWEEN @BegDate AND @Week1End THEN Ind.Price ELSE 0 END) 
PriceVariance,
    (SUM(CASE WHEN Ind.InvoiceDate BETWEEN @Week2Begin AND @EndDate THEN Ind.QtyShipped ELSE 0 
END)  -
    SUM(CASE WHEN Ind.InvoiceDate BETWEEN @BegDate AND @Week1End THEN Ind.Price ELSE 0 END) )
    / 
NULLIF(SUM(CASE WHEN Ind.InvoiceDate BETWEEN @BegDate AND @Week1End THEN Ind.Price ELSE 0 END),0) 
PercentageOfPriceVariance
    From    InvoiceDetail Ind
    Where   Ind.Unit = @Unit
    AND Ind.InvoiceDate BETWEEN @BegDate AND @EndDate
    Group By Ind.Description

我需要添加什么来执行所需的日期数学运算？像这样：

. . .
Select Ind.Description,
    @BegDate  BegDate,
    DATE_ADD(BegDate,INTERVAL 6 DAY) Week1End,
    DATE_ADD(BegDate,INTERVAL 7 DAY)  Week2Begin,
    @EndDate EndDate,
. . .

或者这个：

. . .
DECLARE 
@Week1End datetime = DATE_ADD(BegDate,INTERVAL 6 DAY),
@Week2Begin datetime = DATE_ADD(BegDate,INTERVAL 7 DAY)
. . .

...或者???

更新

好的，这个：

DECLARE @Week1End datetime = DATEADD(Day, 6, @BegDate),
@Week2Begin datetime = DATEADD(Day, 7, @BegDate);

...或者这个：

DECLARE @Week1End datetime = DATEADD(Day, 6, @BegDate),
@Week2Begin datetime = DATEADD(Day, 7, @BegDate)

...或者这个：

DECLARE @Week1End datetime = DATEADD(Day, 6, @BegDate);
DECLARE @Week2Begin datetime = DATEADD(Day, 7, @BegDate);

...现在是（子）问题。

更新 2

它是这样工作的：

DECLARE 
@Week1End datetime = DATEADD(Day, 6, @BegDate),
@Week2Begin datetime = DATEADD(Day, 7, @BegDate);

Answer 1

您只想添加日期吗？

DECLARE @BeginDatePlus6 datetime = DATEADD(dd, 6, begDate)

Answer 2

我想你正在寻找这样的东西：

.
.
Select Ind.Description,
    @BegDate  BegDate,
    DATEADD(day, 6,@BegDate)  Week1End,
    DATEADD(day, 7,@BegDate)  Week2Begin, 
    @EndDate EndDate,

.
.

在此 TSQL 存储过程中进行日期数学运算的正确方法是什么？

What is the correct way to do date math in this TSQL Stored Procedure?

tsql

stored-procedures

date-math

更新

更新 2