如果结束日期比下一行开始日期早 1 天，如何添加日期

问题描述

仅当第一行的结束日期是下一行开始日期的前一天时，我才尝试将两行的天数相加。如果第一行的结束日期不是第二行开始日期的前一天，那么我想从查询中排除这两行。所以在下面的例子中，我应该得到 365 的总和。我的活动表有数千行具有不同的名称和 orderid，我需要在执行此任务的同时保持每个人的 orderID 的完整性。

姓名	订单ID	开始日期	结束日期
乔·史密斯	1	2020-01-01	2020-09-30
乔·史密斯	2	2020-10-01	2020-12-30

解决方法

如果您想要满足条件的多于一行的组，那么这是一种间隙和孤岛问题。

您要做的是为行分配一个“岛”号。您可以通过在前一行达到峰值来查看它是否满足您的条件。如果没有，那么就会出现一个岛屿。岛开始的累计总和为组分配一个岛号。

剩下的就是聚合

select name,min(startdate),max(enddate),datediff(day,max(enddate)) as num_days
from (select t.*,sum(case when prev_end_date <> dateadd(day,-1,startdate) then 0 else 1 end) over 
                 (partition by name order by startdate) as island
      from (select t.*,lag(end_date) over (partition by name order by start_date) as prev_end_date
            from t
           ) t
     ) t
group by name,island
having count(*) > 1;

基于@Gordon-Linoff 的回答以及他关于间隙和岛屿的线索，但我在我的测试数据中添加了错误，如评论中所述。我也用过这个帖子 https://bertwagner.com/posts/gaps-and-islands/

-- test data
DECLARE @t TABLE (name varchar(50),orderID int,StartDate DateTime,EndDate DateTime);

INSERT INTO @t
SELECT 'Joe Smith',1,'2020-01-01','2020-09-30' UNION
SELECT 'Joe Smith',2,'2020-10-01','2020-12-30' UNION
SELECT 'Joe Smith',3,'2021-01-01','2021-09-30' UNION
SELECT 'Joe Smith',4,'2021-10-01','2021-12-31' UNION
SELECT 'Joe Smith',5,'2022-01-01','2022-09-30' UNION
SELECT 'Jane Doe',6,'2020-09-30' UNION
SELECT 'Jane Doe',7,'2020-11-01','2020-12-30';

-- caculate the difference add 1 because EndDate is inclusive (ends on the start of next day)
SELECT t.*,d.IslandStartDate,d.IslandEndDate,DATEDIFF(DAY,IslandStartDate,IslandEndDate) + 1 AS Days FROM (
-- return the minimum and maximum start and end dates 
SELECT
    name,MIN(StartDate) AS IslandStartDate,MAX(EndDate) AS IslandEndDate
FROM (
    SELECT
        *,-- indicates when a new island begins by looking if the current row's StartDate occurs after the previous row's EndDate
        CASE WHEN Groups.PreviousEndDate >= DATEADD(DAY,StartDate) THEN 0 ELSE 1 END AS IslandStartInd,-- indicates which island number the current row belongs to
        SUM(CASE WHEN Groups.PreviousEndDate >= DATEADD(DAY,StartDate) THEN 0 ELSE 1 END) OVER (PARTITION BY name ORDER BY Groups.RN) AS IslandId
    FROM
    (
        -- create a row number column based on the sequence of start and end dates,as well as bring the previous row's EndDate to the current row
        SELECT
            name,orderID,ROW_NUMBER() OVER(PARTITION BY name ORDER BY StartDate,EndDate) AS RN,StartDate,EndDate,LAG(EndDate,1) OVER (PARTITION BY name ORDER BY StartDate,EndDate) AS PreviousEndDate
        FROM
            @t
    ) Groups
) Islands
GROUP BY
    name,IslandId
) d
-- join to get the orderID back
INNER JOIN @t t ON d.name = t.name AND t.StartDate >= d.IslandStartDate AND t.EndDate <= d.IslandEndDate
ORDER BY IslandStartDate,name

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