有没有办法在 PostgreSQL 上计算数值积分？

Question

我有一个包含以下列的表格：timestamp、name 和 activePower。我想据此计算功耗并将其添加到 Grafana 折线图中。

现在，我正在做的是累积和，如下所示：

SELECT
  "timestamp" as time,
  "name", sum("activePower")
    OVER(
      PARTITION BY "name"
      ORDER BY "timestamp"
    ) AS cumulative_sum
FROM   main

不幸的是，timestamp 的间隔不规则，我想做一些类似数值积分的事情（使用梯形规则或其他东西）。

Answer 1

您可以使用lag() 和总和。像这样的：

select m.*,
       sum( (extract(epoch from timestamp) - extract(epoch from prev_timestamp)) * (activePower + prev_activePower) / 2 ) as activePower_seconds
from (select m.*,
             lag(timestamp) over (partition by name order by timestamp) as prev_timestamp,
             lag(activePower) over (partition by name order by activePower) as prev_activePower
      from main m
     ) m;

这使用秒作为水平轴的积分。

Answer 2

虽然被标记为正确，第二行：

lag(activePower) over (partition by name order by activePower)

也应该按时间戳排序。