Grafana、postgresql：聚合函数调用不能包含window个函数调用

Question

在 Grafana 中，我们想要显示指示所选时间间隔内 15 分钟平均值最大值的条形图。我们的数据有规律的 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

要显示指示所选时间间隔内原始值最大值的条柱，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

两种解决方案的天真组合不起作用：

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

我们收到错误：“pq：聚合函数调用不能包含 window 函数调用”。

关于 SO 的建议是使用“with”()，但我不知道在我们的案例中是否适合使用它。

Answer 1

将第一个查询用作第二个查询的 CTE（或 with）。不再需要 CTE 的 order by 子句和第二个查询的 where 子句以及 CTE 的 metric 列。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 table。

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。

Grafana、postgresql：聚合函数调用不能包含window个函数调用

Grafana, postgresql: aggregate function calls cannot contain window function calls

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