在 BigQuery 中按组计算百分位数

Question

四处搜索后，我找不到解决方案。 使用以下示例：

with
  my_data as (
    select 1 as num, 'a' as letter union all
    select 2 as num, 'a' as letter union all
    select 3 as num, 'a' as letter union all
    select 4 as num, 'a' as letter union all
    select 5 as num, 'a' as letter union all
    select 6 as num, 'b' as letter union all
    select 7 as num, 'b' as letter union all
    select 8 as num, 'b' as letter union all
    select 9 as num, 'b' as letter union all
    select 10 as num, 'b' as letter
  )

select
  letter,
  approx_quantiles(num, 100) as value
from my_data
group by letter

我们希望计算num列的 0 - 100 个分位数，按letter分组。 当前查询只返回 2 行，因为value列看起来像一个数组。 我们需要的是上面的查询返回 202 行，结构如下：

letter value pctile
     a     1      0
     a     1      1
     a     1      2
     a     1      3
     a     1      4
...
     b     1      0
     b     1      1
     b     1      2
     b     1      3
     b     1      4

...其中pctile列是 0 - 100，而value列是与pctile列中的百分位数关联的值。 这不是最好的例子，因为我们试图对 0 - 100 个百分位数进行混合，并且示例数据只有 10 行，但是我认为这足以反映问题。

Answer 1

下面是 BigQuery 标准 SQL

#standardSQL
SELECT letter, value, pctile
FROM (
  SELECT
    letter,
    APPROX_QUANTILES(num, 100) AS value
  FROM my_data
  GROUP BY letter
) t, t.value WITH OFFSET AS pctile