Grafana、postgresql：聚合函数调用不能包含窗口函数调用

Question

在 Grafana 中，我们希望显示在所选时间间隔内指示最大 15 分钟平均值的条形。我们的数据有固定的 1 分钟间隔。数据库是 Postgresql。

为了显示 15 分钟的平均值，我们使用以下查询：

SELECT
  timestamp AS time,
  AVG(rawvalue) OVER(ORDER BY timestamp ROWS BETWEEN 7 PRECEDING AND 7 FOLLOWING) AS value,
  '15-min Average' AS metric
FROM database.schema
WHERE $__timeFilter(timestamp) AND device = '$Device'
ORDER BY time

为了在选定的时间间隔内显示表示最大原始值的条形，我们使用以下查询：

SELECT
  $__timeGroup(timestamp,'$INTERVAL') AS time,
  MAX(rawvalue) AS value,
  'Interval Max' AS metric
FROM database.schema
WHERE $__timeFilter(timestamp) AND device = '$Device'
GROUP BY $__timeGroup(timestamp,'$INTERVAL')
ORDER BY time

两种解决方案的简单组合不起作用：

SELECT
  $__timeGroup(timestamp,'$INTERVAL') AS time,
  MAX(AVG(rawvalue) OVER(ORDER BY timestamp ROWS BETWEEN 7 PRECEDING AND 7 FOLLOWING)) AS value,
  'Interval Max 15-min Average' AS metric
FROM database.schema
WHERE $__timeFilter(timestamp) AND device = '$Device'
GROUP BY $__timeGroup(timestamp,'$INTERVAL')
ORDER BY time

我们得到错误：“pq：聚合函数调用不能包含窗口函数调用”。

有一个关于 SO 使用 "with" (Count by criteria over partition) 的建议，但我不知道在我们的案例中使用它是否热门。

Answer 1

将第一个查询用作第二个查询的 CTE（或 with）。 CTE 的order by 子句和第二个查询的where 子句以及CTE 的metric 列不再需要。或者，您可以将第一个查询用作第二个查询的 from 子句中的派生表。

with t as
(
 SELECT
   timestamp AS time,
   AVG(rawvalue) OVER(ORDER BY timestamp ROWS BETWEEN 7 PRECEDING AND 7 FOLLOWING) AS value
 FROM database.schema
 WHERE $__timeFilter(timestamp) AND device = '$Device'
)
SELECT
  $__timeGroup(time,'$INTERVAL') AS time,
  MAX(value) AS value,
  'Interval Max 15-min Average' AS metric
FROM t
GROUP BY 1 ORDER BY 1;

不相关，但 $__timeFilter 和 $__timeGroup 是什么？它们的语义很清楚，但它们来自哪里？顺便说一句，您可能会发现 this 函数很有用。