SAP HANA - 不同行中列值的差异

Question

我有一张下面结构的桌子

ID - Task  | Performed BY | Start Date | End Date  
1 --- Task 3 --- John --------- 9/16/2017 - 9/17/2017  
1 --- Task 2 --- Jim  ----------- 9/14/2017 - 9/16/2017  
1 --- Task 1 --- John  --------- 9/10/2107 - 9/13/2017  
2 --- Task 2 --- Jane --------- 9/14/2017 - 9/15/2017  
2 --- Task 1 --- Claire -------- 9/12/2017 - 9/13/2017  

我需要创建一个新列，显示为SAP HANA中的每个ID执行所有任务所花费的总时间（持续时间）。即最后一个任务的结束日期减去每个ID的第一个任务的开始日期。

以下是我需要的结果：

ID - Task  | Performed BY | Start Date | End Date | Duration  
1 --- Task 3 --- John --------- 9/16/2017 - 9/17/2017 -- 7 Days  
1 --- Task 2 --- Jim  ----------- 9/14/2017 - 9/16/2017 -- 7 Days  
1 --- Task 1 --- John  --------- 9/10/2107 - 9/13/2017 -- 7 Days  
2 --- Task 2 --- Jane --------- 9/14/2017 - 9/15/2017 -- 3 Days  
2 --- Task 1 --- Claire -------- 9/12/2017 - 9/13/2017 -- 3 Days 

这可以使用以下查询在SQL中完成：

SELECT ID，任务，执行者，开始日期，结束日期， DATEDIFF（日， MIN（开始日期）OVER（PARTITION BY ID）， MAX（结束日期）OVER（PARTITION BY ID））持续时间 FROM Table;

我需要使用SAP HANA来执行此任务。我非常感谢有关如何将此SQL查询迁移到HANA的任何帮助。

谢谢！

Answer 1

SAP HANA支持标准SQL window functions，还提供日期计算功能days_between。 您可以像这样编写代码：

SELECT "ID", "Task", "Performed By", "Start Date", "End Date"
     , DAYS_BETWEEN(MIN("Start Date") OVER (PARTITION BY "ID"),
                   MAX("End Date") OVER (PARTITION BY "ID")) "Duration"
FROM tasks
order by "ID", "Task";

ID  Task    Performed By    Start Date  End Date    Duration
1   Task 1  John            10/09/2017  13/09/2017  7       
1   Task 2  Jim             14/09/2017  16/09/2017  7       
1   Task 3  John            16/09/2017  17/09/2017  7       
2   Task 1  Claire          12/09/2017  13/09/2017  3       
2   Task 2  Jane            14/09/2017  15/09/2017  3