Postgres中的分组事件 [英] Grouping Events in Postgres

问题描述

我有一个由用户在网站上的活动生成的事件表：

I've got an events table that is generated by user activity on a site:

timestamp | name
7:00 AM   | ...
7:01 AM   | ...
7:02 AM   | ...
7:30 AM   | ...
7:31 AM   | ...
7:32 AM   | ...
8:01 AM   | ...
8:03 AM   | ...
8:05 AM   | ...
8:08 AM   | ...
8:09 AM   | ...

我想对事件进行汇总，以查看用户何时处于活性。我将有效状态定义为事件发生在+/- 2分钟以内的时间。对于上面的意思是：

I'd like to aggregate over the events to provide a view of when a user is active. I'm defining active to mean the period in which an event is within +/- 2 minutes. For the above that'd mean:

from    | till
7:00 AM | 7:02 AM
7:30 AM | 7:32 AM
8:01 AM | 8:05 AM
8:08 AM | 8:09 AM

编写将以该方法聚合的查询的最佳方法是什么？是可以通过WINDOW函数还是通过自我联接，还是需要PL / SQL？

What's the best way to write a query that'll aggregate in that method? Is it possible via a WINDOW function or self join or is PL/SQL required?

推荐答案

使用两个窗口函数：一个用于计算连续事件（差距）与另一个事件之间的间隔，以找到小于或等于2分钟的一系列差距：

Use two window functions: one to calculate intervals between contiguous events (gaps) and another to find series of gaps less or equal 2 minutes:

select arr[1] as "from", arr[cardinality(arr)] as "till"
from (  
    select array_agg(timestamp order by timestamp)  arr
    from (
        select timestamp, sum((gap > '2m' )::int) over w
        from (
            select timestamp, coalesce(timestamp - lag(timestamp) over w, '3m') gap
            from events
            window w as (order by timestamp)
            ) s
        window w as (order by timestamp)
        ) s
    group by sum
    ) s

   from   |   till   
----------+----------
 07:00:00 | 07:02:00
 07:30:00 | 07:32:00
 08:01:00 | 08:05:00
(3 rows)        

在此处进行测试。

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