如何在postgresql中引導？

-1

id  task_start_time   task_end_time 
__  _______________   _____________ 
1  2017-03-21 00:09:10  2017-03-21 00:12:18 
1  2017-03-21 00:12:19  2017-03-21 00:12:56 
1  2017-03-21 00:12:57  2017-03-21 00:13:10 
2  2017-03-21 10:09:10  2017-03-21 10:25:34 
2  2017-03-21 10:25:34  2017-03-21 11:09:10 
2  2017-03-21 11:09:10  2017-03-21 11:21:39 
3  2017-03-21 12:09:10  2017-03-21 12:19:19 
3  2017-03-21 12:19:19  2017-03-21 12:29:19 
3  2017-03-21 12:29:10  2017-03-21 12:39:10

從這個表我需要通過添加另一列是特定的ID task_end_time這是id的task_end_time的上一行更新表。

id  task_start_time   task_end_time  previous_task_end_time 

__  _______________   _____________  ______________________ 
1  2017-03-21 00:09:10  2017-03-21 00:12:18    NA 
1  2017-03-21 00:12:19  2017-03-21 00:12:56    2017-03-21 00:12:18 
1  2017-03-21 00:12:57  2017-03-21 00:13:10    2017-03-21 00:12:56 
2  2017-03-21 10:09:10  2017-03-21 10:25:34    2017-03-21 10:25:34 
2  2017-03-21 10:25:34  2017-03-21 11:09:10    2017-03-21 11:09:10 
2  2017-03-21 11:09:10  2017-03-21 11:21:39    2017-03-21 11:21:39 
3  2017-03-21 12:09:10  2017-03-21 12:19:19    2017-03-21 12:19:19 
3  2017-03-21 12:19:19  2017-03-21 12:29:19    2017-03-21 12:29:19 
3  2017-03-21 12:29:10  2017-03-21 12:39:10    2017-03-21 12:39:10

所以可以在postgresql中輕鬆完成，或者我需要使用JAVA來實現這個嗎？任何幫助表示讚賞。

來源

2017-05-26 Ricky

使用window functionlag。

SELECT id, task_start_time, task_end_time 
    , LAG(task_end_time) OVER (PARTITION BY id ORDER BY task_end_time) AS previous_task_end_time 
    FROM ...

有關運行示例，請參見SQL Fiddle。

id task_start_time   task_end_time   previous_task_end_time 
1 2017-03-21 00:09:10  2017-03-21 00:12:18  (null) 
1 2017-03-21 00:12:19  2017-03-21 00:12:56  2017-03-21 00:12:18 
1 2017-03-21 00:12:57  2017-03-21 00:13:10  2017-03-21 00:12:56 
2 2017-03-21 10:09:10  2017-03-21 10:25:34  (null) 
2 2017-03-21 10:25:34  2017-03-21 11:09:10  2017-03-21 10:25:34 
2 2017-03-21 11:09:10  2017-03-21 11:21:39  2017-03-21 11:09:10 
3 2017-03-21 12:09:10  2017-03-21 12:19:19  (null) 
3 2017-03-21 12:19:19  2017-03-21 12:29:19  2017-03-21 12:19:19 
3 2017-03-21 12:29:10  2017-03-21 12:39:10  2017-03-21 12:29:19

來源

2017-05-26 06:19:45 Andreas

非常感謝一個簡單的問題做這個工程的更新通過更改SQL成'更新...設定previous_task_end_time = LAG（task_end_time）OVER（PARTITION BY ID ORDER BY task_end_time）' – Ricky

號對於更新的嘗試'UPDATE mytable a SET previous_task_end_time =（SELECT MAX（b.task_end_time）FROM mytable b WHERE b.id = a.id AND b.task_end_time Andreas

如何在postgresql中引導？

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