BigQuery：如何在窗口函数上合并 HLL 草图？（计算滚动窗口上的不同值）

Question

示例相关表架构：

+---------------------------+-------------------+
| activity_date - TIMESTAMP | user_id - STRING  |
+---------------------------+-------------------+
| 2017-02-22 17:36:08 UTC   | fake_id_i24385787 |
+---------------------------+-------------------+
| 2017-02-22 04:27:08 UTC   | fake_id_234885747 |
+---------------------------+-------------------+
| 2017-02-22 08:36:08 UTC   | fake_id_i24385787 |
+---------------------------+-------------------+

我需要在滚动时间段（90 天）内对大型数据集的活跃不同用户进行计数，并且由于数据集的大小而遇到问题。

起初，我尝试使用窗口函数，类似于这里的答案。 /sf/answers/1930213211/

WITH
  daily AS (
  SELECT
    DATE(activity_date) day,
    user_id
  FROM
    `fake-table`)
SELECT
  day,
  SUM(APPROX_COUNT_DISTINCT(user_id)) OVER (ORDER BY day ROWS BETWEEN 89 PRECEDING AND CURRENT ROW) ninty_day_window_apprx
FROM
  daily
GROUP BY
  1
ORDER BY
  1 DESC

然而，这会导致每天获得不同数量的用户，然后将它们相加 - 但如果它们出现多次，则可以在窗口内复制不同的用户。因此，这并不是对 90 天内不同用户的真正准确衡量。

我尝试的下一件事是使用以下解决方案 /sf/answers/3336171331/ - 将每个窗口的所有不同 user_id 连接到一个数组，然后计算其中的不同。

WITH daily AS (
  SELECT date(activity_date) day, STRING_AGG(DISTINCT user_id) users
  FROM `fake-table`  
  GROUP BY day
), temp2 AS (
  SELECT
    day, 
    STRING_AGG(users) OVER(ORDER BY UNIX_DATE(day) RANGE BETWEEN 89 PRECEDING AND CURRENT ROW) users
  FROM daily
)

SELECT day, 
  (SELECT APPROX_COUNT_DISTINCT(id) FROM UNNEST(SPLIT(users)) AS id) Unique90Days
FROM temp2

order by 1 desc

然而，这很快就用完了任何大的内存。

接下来是使用 HLL 草图以更小的值来表示不同的 ID，因此内存将不是问题。我以为我的问题已解决，但在运行以下命令时出现错误：错误只是“不支持函数 MERGE_PARTIAL”。我也尝试过 MERGE 并得到同样的错误。它仅在使用窗口函数时发生。为每一天的价值创建草图工作正常。

我通读了 BigQuery 标准 SQL 文档，但没有看到任何关于 HLL_COUNT.MERGE_PARTIAL 和 HLL_COUNT.MERGE 的窗口函数。大概这应该将 90 个草图合并成一个 HLL 草图，代表 90 个原始草图之间的不同值？

WITH
  daily AS (
  SELECT
    DATE(activity_date) day,
    HLL_COUNT.INIT(user_id) sketch
  FROM
    `fake-table`
  GROUP BY
    1
  ORDER BY
    1 DESC),

  rolling AS (
  SELECT
    day,
    HLL_COUNT.MERGE_PARTIAL(sketch) OVER (ORDER BY UNIX_DATE(day) RANGE BETWEEN 89 PRECEDING AND CURRENT ROW) rolling_sketch
    FROM daily)

SELECT
  day,
  HLL_COUNT.EXTRACT(rolling_sketch)
FROM
  rolling
ORDER BY
  1 

“错误图像 - 不支持函数 MERGE_PARTIAL”

任何想法为什么会发生此错误或如何调整？

Answer 1

下面是 BigQuery 标准 SQL，使用窗口函数完全符合您的要求

#standardSQL
SELECT day,
  (SELECT HLL_COUNT.MERGE(sketch) FROM UNNEST(rolling_sketch_arr) sketch)  rolling_sketch
FROM (
  SELECT day, 
    ARRAY_AGG(ids_sketch) OVER(ORDER BY UNIX_DATE(day) RANGE BETWEEN 89 PRECEDING AND CURRENT ROW) rolling_sketch_arr 
  FROM (
    SELECT day, HLL_COUNT.INIT(id) ids_sketch
    FROM `project.dataset.table`
    GROUP BY day
  )
)

您可以使用 [totally] 虚拟数据进行测试和使用，如下例所示

#standardSQL
WITH `project.dataset.table` AS (
  SELECT 1 id, DATE '2019-01-01' day UNION ALL
  SELECT 2, '2019-01-01' UNION ALL
  SELECT 3, '2019-01-01' UNION ALL
  SELECT 1, '2019-01-02' UNION ALL
  SELECT 4, '2019-01-02' UNION ALL
  SELECT 2, '2019-01-03' UNION ALL
  SELECT 3, '2019-01-03' UNION ALL
  SELECT 4, '2019-01-03' UNION ALL
  SELECT 5, '2019-01-03' UNION ALL
  SELECT 1, '2019-01-04' UNION ALL
  SELECT 4, '2019-01-04' UNION ALL
  SELECT 2, '2019-01-05' UNION ALL
  SELECT 3, '2019-01-05' UNION ALL
  SELECT 5, '2019-01-05' UNION ALL
  SELECT 6, '2019-01-05' 
)
SELECT day,
  (SELECT HLL_COUNT.MERGE(sketch) FROM UNNEST(rolling_sketch_arr) sketch)  rolling_sketch
FROM (
  SELECT day, 
    ARRAY_AGG(ids_sketch) OVER(ORDER BY UNIX_DATE(day) RANGE BETWEEN 2 PRECEDING AND CURRENT ROW) rolling_sketch_arr 
  FROM (
    SELECT day, HLL_COUNT.INIT(id) ids_sketch
    FROM `project.dataset.table`
    GROUP BY day
  )
)
-- ORDER BY day

结果

Row day         rolling_sketch   
1   2019-01-01  3    
2   2019-01-02  4    
3   2019-01-03  5    
4   2019-01-04  5    
5   2019-01-05  6