在mysql查询中计算日期和持续时间 [英] Compute dates and durations in mysql query

问题描述

我有一个示例表(table_name:track_task)，如下所示:

I have a sample table (table_name: track_task) like below:

task_id     stage        log_date
----------------------------------------
   3          1      2011-06-01 08:36:21
   9          1      2011-06-03 12:35:47
   3          2      2011-06-05 14:25:42
  21          1      2011-06-11 13:03:34
   9          2      2011-06-11 15:25:57
   3          3      2011-06-12 10:16:09
  21          2      2011-06-15 15:30:29
   3          4      2011-06-22 15:34:33
  21          3      2011-06-23 12:53:49
   9          4      2011-06-25 16:25:08

当应用程序代码中的某些操作使任务阶段进展时，以上数据将自动填充.阶段从1到4.但是，由于某种逻辑，任务可能会跳过阶段3.但是所有任务都将在阶段4结束.可能的任务路径如下:

The data above is automatically populated when a task stage is progressed by some action in the application code. The stages run from 1 to 4. However, due to some logic, a task may skip stage 3. But all tasks end at stage 4. Probable task paths are like so:

(1,2,3,4) / (1,2,4) - Completed tasks
(1,2,3) / (1,2)     - In progress tasks

我需要查询和检索一个报告，该报告显示任务在给定时间的每个阶段需要多长时间(以天为单位).到目前为止，我已经提出了以下查询:

I need to query and retrieve a report that shows how long (in days) a task takes in each stage at a given time. I have come up with the following query so far:

SELECT z.task_id, a.log_date begin_date, d.log_date end_date, 
       DATEDIFF( b.log_date, a.log_date ) step1_days, 
       DATEDIFF( c.log_date, b.log_date ) step2_days, 
       DATEDIFF( d.log_date, c.log_date ) step3_days, 
       DATEDIFF( d.log_date, a.log_date ) cycle_days
FROM track_task z
LEFT JOIN track_task a ON ( z.task_id = a.task_id AND a.staging_id =1 )
LEFT JOIN track_task b ON ( z.task_id = b.task_id AND b.staging_id =2 )
LEFT JOIN track_task c ON ( z.task_id = c.task_id AND c.staging_id =3 )
LEFT JOIN track_task d ON ( z.task_id = d.task_id AND d.staging_id =4 )
GROUP BY z.oppty_id

得出如下结果集:

task_id  begin_date   end_date   step1_days  step2_days  step3_days  cycle_days
-------------------------------------------------------------------------------
  3      2011-06-01  2011-06-22       4          7          10           21
  9      2011-06-03  2011-06-25       8         NULL       NULL          22
 21      2011-06-11     NULL          4          8         NULL         NULL

这是解决问题的好方法还是更好的方法?如何将NULL值报告为零?我如何才能检索到仍在进行中的任务的end_date?

Is this a good way to go about it or there is a better way? How can I have the NULL values reported as zero? How can I retrieve then end_date for a task that is still in progress?

推荐答案

那是关于我将如何做这样的事情，假设每个task只会使用一个stage的实例(如果没有的话) ，您需要做更多的工作，包括定义需求和编写查询).

That looks about How I would do something like this, assuming there's only going to ever be one instance of a stage used per task (if not, you need more work, both in defining your requirements, and writing the query).

要使null显示为0，请使用COALESCE()功能:

To make null appear as 0, use the COALESCE() function:

SELECT z.task_id, COALESCE(DATEDIFF(b.log_date, a.log_date), 0) as step1_days

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