如何在SQL Server中获取日期的差异

Question

如果ID是最低和最新和最差的两个记录之间的差异，我无法编写查询以获取UpdateDate和2条记录的CreationDate之间的差异最近UpdateDate。 这里是我的查询：

SELECT 
    a.ID, a.RequestID, b.KrStatus, b.CrDate , b.UpdateDate, 
    DATEDIFF (HOUR, b.CrDate, b.UpdateDate) AS TimeDifference, 
CASE WHEN a.ID = (SELECT MAX(a.ID) FROM [dbo].[Krdocs_hist] a WHERE a.RequestID = 1) 
    THEN 'YES' 
    ELSE 'NO' 
END AS isMax, 
CASE WHEN a.ID = (SELECT MIN(a.ID) FROM [dbo].[Krdocs_hist] a WHERE a.RequestID = 1) 
    THEN 'YES' 
    ELSE 'NO' 
END AS isMi 
FROM [dbo].[Krdocs_hist] a, [dbo].Krdocs_Details_hist b 
WHERE 
    a.RequestId = b.RequestId 
    and a.ID = b.ID 
    and a.RequestId = 1 
ORDER BY b.RequestID 

这里是我当前的结果：

我想要做的就是最后可能记录，检查是否存在之前已经存在。如果没有比较UpdateDate和的crdate（UpdateDate负的crdate如果有这个，我想要做的UpdateDate减去前UpdateDate之前的纪录

使用此查询：。

SELECT b.Id, b.RequestId, b.UpdateDate, b.KrStatus 
FROM [dbo].[Krdocs_Details_hist] b 
WHERE b.RequestId = 1 

有这结果：

而且使用此查询：

SELECT a.* 
FROM [dbo].[Krdocs_hist] a 
WHERE RequestId = 1 

有这样的结果：

Answer 1

UPDATE 由于LAG可从2012 SQL，您可以使用如下：

SELECT 
     ID, 
     RequestID, 
     CrDate, 
     UpdateDate, 
     KrStatus, 
     DATEDIFF(HOUR, PreviousUpdateDate, UpdateDate) as TimeDifference 
FROM 
    (SELECT 
     ID, 
     RequestID, 
     CrDate, 
     UpdateDate, 
     KrStatus, 
     LAG(UpdateDate, 1, CrDate) OVER (ORDER BY YEAR(ID)) AS PreviousUpdateDate 
    FROM [dbo].Krdocs_Details_hist) as tmp 

我想你可以尝试这样的：

SELECT 
    CASE 
     WHEN COUNT(*) <= 1 THEN DATEDIFF(HOUR, 
      (SELECT CrDate FROM [dbo].Krdocs_Details_hist), 
      (SELECT UpdateDate FROM [dbo].Krdocs_Details_hist)) 
     WHEN COUNT(*) > 1 THEN DATEDIFF(HOUR, 
      (SELECT MAX(UpdateDate) FROM [dbo].Krdocs_Details_hist WHERE UpdateDate < (SELECT MAX(UpdateDate) FROM [dbo].Krdocs_Details_hist)), 
      (SELECT MAX(UpdateDate) FROM [dbo].Krdocs_Details_hist)) 
    END AS TimeDifference 
FROM [dbo].Krdocs_Details_hist