SQL中时间序列数据的导数/时间差

Question

我正在查询一个请求数据集，并希望在服务请求之间获得“正常运行时间”。这篇文章Discrete Derivative in SQL 几乎就是我所追求的。但是，我正在处理日期时间数据，我不相信我可以假设工作订单将按时间顺序排序。另外，我对每个请求都有特定的位置。

Request	Location	RequestDate	CompleteDate
R-001	a	1/1/2020	1/5/2020
R-002	a	3/17/2020	3/20/2020
R-004	b	2/27/2020	3/1/2020
R-003	b	4/22/2020	4/23/2020
R-005	a	7/3/2020	7/7/2020

我确实看到了SQL DATEDIFF() 函数。 以下是对引用帖子中顶级答案的轻微修改。

Select a.RequestDate as StartTime
     , b.CompleteDate as EndTime
     , DATEDIFF(b.RequestDate-a.CompleteDate) as TimeChange
FROM YourTable a 
Left outer Join YourTable b ON b.time>a.time
Left outer Join YourTable c ON c.time<b.time AND c.time > a.time
Where c.time is null
Order By a.RequestDate

另外，我有点掌握两次别名同一张表但不完全。我也不明白外部连接。 最终，我想要新的专栏……如果这样可以简化问题，我可以提前做出假设或按请求日期排序。

Request	Location	RequestDate	CompleteDate	Up-Time
R-001	a	1/1/2020	1/5/2020	null
R-002	a	3/17/2020	3/20/2020	72
R-004	b	2/27/2020	3/1/2020	null
R-003	b	4/22/2020	4/23/2020	52
R-005	a	7/3/2020	7/7/2020	105

我希望它与原始帖子没有太大不同，其中按位置分组并按请求日期排序。

Answer 1

这使用 LAG 窗口函数来分别执行每个位置的此 RequestDate 和上一个 CompleteDate 之间的差异（以天为单位），按 RequestDate 排序（这里有一些假设）。

CREATE TABLE log (
    Request      VARCHAR(30)
  , Location     VARCHAR(10)
  , RequestDate  date
  , CompleteDate date
);

INSERT INTO log VALUES 
  ('R-001', 'a',  '2020-1-1',    '2020-1-5' )
, ('R-002', 'a',  '2020-3-17',   '2020-3-20')
, ('R-004', 'b',  '2020-2-27',   '2020-3-1' )
, ('R-003', 'b',  '2020-4-22',   '2020-4-23')
, ('R-005', 'a',  '2020-7-3',    '2020-7-7' )
;

查询：

SELECT log.*
     , LAG(CompleteDate) OVER (PARTITION BY Location ORDER BY RequestDate) AS prev_date
     , RequestDate - LAG(CompleteDate) OVER (PARTITION BY Location ORDER BY RequestDate) AS diff
  FROM log
 ORDER BY Location, RequestDate 
;

结果：

Working test case

用于解决字符串到日期转换问题的附加 SQL (PostgreSQL)：

WITH logs AS (
        SELECT Request, Location
             , TO_DATE(RequestDate, 'MM/DD/YYYY')  AS RequestDate
             , TO_DATE(CompleteDate, 'MM/DD/YYYY') AS CompleteDate
          FROM log
     )
SELECT log.*
     , LAG(CompleteDate) OVER (PARTITION BY Location ORDER BY RequestDate) AS prev_date
     , RequestDate - LAG(CompleteDate) OVER (PARTITION BY Location ORDER BY RequestDate) AS diff
  FROM logs AS log
 ORDER BY Location, RequestDate 
;

The updated working test case