Esper：为在另一个事件之后发生的事件创建窗口

问题描述

我想要在不同的功率设置1-10（sensor = 2）下的平均速度（sensor = 1）。我不希望传感器1的速度出现在设置更改（sensor = 2）之前的平均值计算中。

例如power_setting = 1，速度= 50，速度= 60，power_setting = 2，速度= 100，速度= 120

如果我在power_setting = 2周围有一个时间窗口，那么它可能包括power_setting = 1的速度。

我如何明确告诉esper仅使用功率设置更改后出现的值进行计算。

这是我当前的脚本：

CREATE window SpeedWindow.win:time_batch(30 sec) as (speed double,power_setting int);

INSERT into SpeedWindow
SELECT
    speedEvent.value as speed,powerSetting.value as power_setting
FROM
    Sensors(id = 1).std:lastevent() as speedEvent,Sensors(id = 2).std:lastevent() as powerSetting;

INSERT into Output
SELECT
    case
        when SpeedWindowEvent.power_setting = 1 then 4154
        when SpeedWindowEvent.power_setting = 2 then 4155
        ... etc ...
    end as id,avg(SpeedWindowEvent.speed) as value
FROM
    SpeedWindow as SpeedWindowEvent
GROUP BY
    SpeedWindowEvent.power_setting;

解决方法

基于阐明用例的注释。创建一个在速度事件上启动和终止的上下文。

// make it easy to read,takes no CPU at all
insert into Speed select * from Sensor(id=1);
insert into Power select * from Sensor(id=2);

create context SpeedSession initiated by Speed terminated by Speed;
context SpeedSession select avg(...) from Power;