SQL 服务器 DATEADD 特定工作日

Question

所以我需要在日期中添加一些天数，比如 30 天，但是 30 天不能是日历日，它们是依赖于某些背后逻辑的参数，所以，我需要找到一种方法来例如，在星期一和星期三之间添加 30 天的日期：如果我在 2 月 15 日加上 30（周一到周三）天，我应该得到 4 月 26 日如果我在 2 月 15 日加上 30（周日到周五）天，我应该得到 3 月 17 日

如果情况不够清楚，请告诉我，我会尽力给出更好的解释。

谢谢。

Answer 1

我会用递归 CTE 来做，像这样：

-- 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

以上查询是针对 Mon-Wed 的。要使其 Sun-Friday 在 CTE

的日子里修改活动标志

Answer 2

首先，我生成了 StartDate 和 EndDate 之间的一系列日期，但 returns 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)

然后您可以使用一个简单的 WHERE IN () 来 select 您想要包括的星期几，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);

注意你的 SQL 服务器中一周的第一天，你可以用 SET DATEFIRST 更改它。

在这里查看：http://rextester.com/WCLIXM28868

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