SQL server DATEADD特定的周日

Question

所以我需要添加一些日期，比如说30，但30天不能是日历天，它们是依赖于某些逻辑的参数，所以我需要找到一种方法来添加日期之间星期三和星期三之间的30天，例如： 如果我添加30（星期三到星期三）到2月15日，我应该得到4月26日 如果我添加30（太阳到星期五） 15日，我应该得到3月17日

如果情况不够清楚，让我知道蚂蚁我会尽力给出一个更好的解释。

谢谢。

Answer 1

我第一次产生了一系列的起始日期和结束日期之间的日期，但它返回星期几：

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) 

然后你可以使用一个简单的WHERE IN（）来选择你想包含的星期几，并计算返回的日期。

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); 

时请小心您的SQL Server一周的冷杉一天，你可以用SET DATEFIRST改变它。

请在此检查：http://rextester.com/WCLIXM28868

Answer 2

我会用递归CTE，这样做：

-- 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 

以上查询是周一至周三为了让孙周五修改的有效标志在天CTE