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任意时间段的差值分析

需求描述

在智能用电中，每个电表的用电量记录都是按频率收集的。

例如，收集频率是每 10分钟一次（可能以秒、分钟和小时为单位）。分析时，需要统计这个时间范围内的用电量（结束时间用电量减去开始时间用电量），会按照小时、日、月、年等不同维度进行显示。

在仪表板中实现

原有统计数据示例如下，每十分钟统计一次。

实际每个时间段的用电量需要用下一行的数据减去当前行。

这里我们需要创建一个数据列，使每一行都返回数据。用窗口函数 LEADW拿到下一行的数据，然后再减去当前数据。

LEADW(
    null,
    'GrapecityElectricityData_Direct'[Electricity Value],
    PARTITIONBY(
        'GrapecityElectricityData_Direct'[Device ID]
        ),
    ORDERBY(
        'GrapecityElectricityData_Direct'[Collection DateTime]
        )
    )
-
'GrapecityElectricityData_Direct'[Electricity Value]

绑定实际用电量，可见每一行得到的都是下一行的值减去当前行。

这样就得到了每一个10分钟的用电量，后续可使用该数据进行按天，月等维度进行统计。（下图中的 leadwcal 即实际用电量）

type=info
提示
使用 leadw 进行计算时会存在一定误差，因为最后一行在计算时没有下一行来参与运算，所以无法正确返回结果。