SQL-試圖從同一列中減去日期值

Question

我需要將最大日期減去上一個以前的狀態日期，並且不能算出來。我將使用FindingID和UpdatedEstimatedRemediationDate。

例如：

FindingID 'FND-5645' 已經更新3次：

UpdatedEstimatedRemediationDate 
-------------------------------- 
NULL 
2015-06-15 
2015-12-30 
2016-06-30 

我需要從12,2015月獲得2016年6月30日，天差。我正在使用SQL Server 2008 R2。提前致謝。

Answer 1

可以使用ROW_NUMBER()通過FindingId和秩序由UpdateDate遞減分區，挑選第一個和最後日期，在該日期DIFF天：

設置：

-- drop table UpdatedEstimatedRemediationDate 
create table UpdatedEstimatedRemediationDate 
(
    FindingId INT, 
    UpdateDate DATE 
) 

insert into UpdatedEstimatedRemediationDate values 
(1, '2015-06-15'), (1, '2015-12-30'), (1, '2016-06-30'), (2, '2015-07-13'), (2, '2016-05-01') 
GO 

查詢：

;WITH Cte AS (
    SELECT FindingId, UpdateDate, ROW_NUMBER() OVER (PARTITION BY FindingId ORDER BY UpdateDate DESC) AS RowNo 
    FROM UpdatedEstimatedRemediationDate 
) 
SELECT LU1.FindingId, DATEDIFF(day, LU1.UpdateDate, LU2.UpdateDate) AS DaysDiff 
FROM Cte LU1 
    JOIN Cte LU2 ON LU2.FindingId = LU1.FindingId AND LU1.RowNo = 2 AND LU2.RowNo = 1 

[沒有自我加入版]

對於SQL Server 2012，SELF JOIN可使用LAG/LEAD功能避免：

WITH CTE AS (
    SELECT FindingId, DATEDIFF(day, UpdateDate, LEAD(UpdateDate, 1, NULL) OVER (PARTITION BY FindingId ORDER BY UpdateDate)) DayDiff, 
     ROW_NUMBER() OVER (PARTITION BY FindingId ORDER BY UpdateDate DESC) RowNo 
FROM UpdatedEstimatedRemediationDate) 
SELECT CTE.FindingId, CTE.DayDiff 
FROM CTE 
WHERE RowNo = 2 

Answer 2

如果我理解正確的，這基本上是一個集合的查詢與datediff()：

select findingid, datediff(day, min(UpdatedEstimatedRemediationDate), max(UpdatedEstimatedRemediationDate) 
from t 
group by findingid;