如何使此查询高效运行

Question

在BigQuery中，我们试图运行：

SELECT day, AVG(value)/(1024*1024) FROM ( 
    SELECT value, UTC_USEC_TO_DAY(timestamp) as day, 
         PERCENTILE_RANK() OVER (PARTITION BY day ORDER BY value ASC) as rank 
    FROM [Datastore.PerformanceDatum]
    WHERE type = "MemoryPerf"
) WHERE rank >= 0.9 AND rank <= 0.91 
GROUP BY day 
ORDER BY day desc;

其返回相对少量的数据。但我们得到的信息是：

Error: Resources exceeded during query execution. The query contained a GROUP BY operator, consider using GROUP EACH BY instead. For more details, please see https://developers.google.com/bigquery/docs/query-reference#groupby

是什么导致这个查询失败，子查询的大小？我们是否可以做一些等效的查询来避免这个问题？

---

编辑以响应注释：如果我添加GROUP EACH BY（并删除外部ORDER BY），则查询失败，声称GROUP EACH BY在这里不可并行。

Answer 1

我写了一个对我有效的等价查询：

SELECT day, AVG(value)/(1024*1024) FROM (
SELECT data value, UTC_USEC_TO_DAY(dtimestamp) as day, 
         PERCENTILE_RANK() OVER (PARTITION BY day ORDER BY value ASC) as rank 
    FROM [io_sensor_data.moscone_io13]
    WHERE sensortype = "humidity"
) WHERE rank >= 0.9 AND rank <= 0.91 
GROUP BY day 
ORDER BY day desc;

如果我只运行内部查询，我会得到3660624个结果。你的数据集比这个大吗？

当按天分组时，外部选择只给我4个结果。我会尝试不同的分组，看看我是否能达到极限：

SELECT day, AVG(value)/(1024*1024) FROM (
SELECT data value, dtimestamp / 1000 as day, 
         PERCENTILE_RANK() OVER (PARTITION BY day ORDER BY value ASC) as rank 
    FROM [io_sensor_data.moscone_io13]
    WHERE sensortype = "humidity"
) WHERE rank >= 0.9 AND rank <= 0.91 
GROUP BY day 
ORDER BY day desc;

现在有57862个不同的小组参加。

我尝试了不同的组合以得到相同的错误。我得到的错误与您将初始数据量增加一倍的错误相同。一个简单的"破解"使数据量翻倍的方法正在改变：

    FROM [io_sensor_data.moscone_io13]

收件人：

    FROM [io_sensor_data.moscone_io13], [io_sensor_data.moscone_io13]

然后我得到了同样的错误。你有多少数据？你能应用一个额外的过滤器吗？由于您已经按天对percentile_rank进行了分区，您是否可以添加一个额外的查询来只分析一小部分天数（例如，仅上个月）？