SQL Server DATEADD特定的工作日

Question

因此，我需要在日期中添加一些日期，例如30天，但30天不能是日历日，它们是取决于背后某些逻辑的参数，因此，我需要找到一种方法来添加日期30例如，星期一至星期三之间的天数：如果我在2月15日前加上30（星期一至星期三）天，则应该是4月26日。如果我在2月15日前加上30（星期日至星期五）几天，则应该是3月17日。

如果情况还不清楚，请让我知道蚂蚁，我将尝试给出更好的解释。

谢谢。

Answer 1

我将使用递归CTE来做到这一点，例如：

-- set datefirst as Sunday. You may need to adjust it ot the correct Datefirst value for your locale
SET DATEFIRST 7

declare @d datetime
set @d = '2017-02-15'
SELECT @d

;with 
days as( 
-- this CTE where you define the active days. The days start 
select 1 as d, 0 as active -- sunday
union
select 2 as d, 1 as active -- monday
union 
select 3 as d, 1 as active
union 
select 4 as d, 1 as active
union 
select 5 as d, 0 as active
union 
select 6 as d, 0 as active 
union
select 7 as d, 0 as active -- saturday

),
n as (
select CASE WHEN DATEPART(dw, DATEADD(d, 1, @d)) IN (select d from days where active=1) THEN 1 ELSE 0 END as n, @d as dt
union all 
select CASE WHEN DATEPART(dw, DATEADD(d, 1, dt)) IN (select d from days where active=1) THEN n+1 else n end, DATEADD(d, 1, dt)
from n where n < 30)
--SELECT * from n order by n
SELECT top 1 @d = dt from n order by n desc

select @d

上面的查询适用于周一至周三。 为了使其成为星期日至星期五，请修改CTE天内的有效标记

Answer 2

首先，我在StartDate和EndDate之间生成了一系列日期，但返回的是“星期几”：

SELECT  DATEPART(weekday, DATEADD(DAY, nbr - 1, @StartDate)) as dow
FROM    (SELECT    ROW_NUMBER() OVER ( ORDER BY c.object_id ) AS Nbr
         FROM      sys.columns c
         )nbrs
WHERE   nbr - 1 <= DATEDIFF(DAY, @StartDate, @EndDate)

然后，您可以使用简单的WHERE IN（）选择要包含的星期几，并计算返回的天数。

DECLARE @StartDate DATE = '20170101'
        , @EndDate DATE = '20170131'

SELECT COUNT(*) AS DAYS
FROM (
        SELECT  DATEPART(weekday, DATEADD(DAY, nbr - 1, @StartDate)) as dow
        FROM    (SELECT    ROW_NUMBER() OVER ( ORDER BY c.object_id ) AS Nbr
                 FROM      sys.columns c
                )nbrs
        WHERE   nbr - 1 <= DATEDIFF(DAY, @StartDate, @EndDate)
    ) T1
WHERE DOW IN (3,4,5);

在您的SQL Server中，请注意每周的第一天，您可以使用SET DATEFIRST进行更改。

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