Question

当从商店购买商品时，我有一个BigQuery表记录。它包含ItemID和时间戳。我对购买的每件商品的运行总数感兴趣。我有这个查询生成运行总计：

SELECT ItemID,timestamp,count(*)
OVER
  (PARTITION BY ItemID
  ORDER BY timestamp ASC, ItemID) AS runningtotal
from 
(
  SELECT * FROM [mydb.purchases] 
)
ORDER BY timestamp

此表包含数十万行。我现在要做的是花一段时间（例如一周），并获得该周内每个ItemID的100个运行总计样本（为了绘制没有太多数据点的图表）。我不知道该怎么做。我可以通过过滤“where（rownumber％（rowcount / 100）= 0”这样的东西来获得100个样本但是如何为表中的每个ItemID执行此操作？我是否需要为每个ItemID执行多个子查询然后创建工会？谢谢

Answer 1

使用标准SQL，您可以首先使用LIMIT函数内的ARRAY_AGG子句收集100个时间戳的样本：

#standardSQL
SELECT ItemID, timestamp, COUNT(*)
OVER (PARTITION BY ItemID ORDER BY timestamp ASC) AS running_total
FROM (
SELECT ItemID, ARRAY_AGG(timestamp LIMIT 100) timestamps
FROM `mydb.purchases`) t, t.timestamps timestamp
ORDER BY timestamp

如果这不进行随机抽样，您可以使用RAND()重新调整时间戳：

#standardSQL
SELECT ItemID, timestamp, COUNT(*)
OVER (PARTITION BY ItemID ORDER BY timestamp ASC) AS running_total
FROM (
SELECT ItemID, ARRAY_AGG(timestamp ORDER BY RAND() LIMIT 100) timestamps
FROM `mydb.purchases`)  t, t.timestamps timestamp
ORDER BY timestamp

Answer 2

以下是您在抽样意义上所描述的内容我将selecting week worse of data方面排除在外，因为它是微不足道的

#standardSQL
SELECT
  ItemID,
  timestamp,
  runningtotal  
FROM (
  SELECT 
    ItemID, 
    timestamp, 
    COUNT(1) OVER (PARTITION BY ItemID ORDER BY timestamp ASC) AS runningtotal,
    ROW_NUMBER() OVER (PARTITION BY ItemID ORDER BY timestamp ASC) AS rownumber,
    COUNT(1) OVER(PARTITION BY ItemID) AS rowcount
  FROM `mydb.purchases`
)
WHERE MOD(rownumber, CAST(rowcount/100 AS INT64)) = 0
-- ORDER BY ItemID, timestamp

BigQuery：如何随时间推移运行总计

2 个答案: