未定义行数的计算

Question

考虑到我们可以有一、二、三或更多行，我想添加一个计算。我们可以使用关系获取所有数据，但我有点卡住了，因为关系的数量是未定义的。 例如，作为来源：

SELECT 123 AS id
      ,250 AS amount
      ,225 AS debt
      ,NULL AS relation
      ,1 AS rn
UNION ALL    
SELECT 124 AS id
      ,150 AS amount
      ,25 AS debt
      ,123 AS relation
      ,2 AS rn
UNION ALL   
SELECT 125 AS id
      ,160 AS amount
      ,50.25 AS debt
      ,124 AS relation
      ,3 AS rn
UNION ALL
SELECT 126 AS id
      ,80 AS amount
      ,25 AS debt
      ,125 AS relation
      ,4 AS rn 

源表

id	amount	debt	relation	rn
123	250	225	NULL	1
124	150	25	123	2
125	160	50.25	124	3
126	80	25	125	4

茶几

id	amount	debt	relation	rn	cal
123	250	225	NULL	1	250
124	150	25	123	2	22.5
125	160	50.25	124	3	7.5375
126	80	25	125	4	3.75

我需要应用如下计算：

• 第 1 行：金额
• 第 2 行：row2.debt*row1.debt/row1.amount
• 第 3 行：row3.debt*row2.debt/row2.amount*row1.debt/row1.amount
• 第 4 行：row4.debt*row3.debt/row3.debt*row2.debt/row2.amount*row1.debt/row1.amount
• 等等..

我正在使用 dbt，但很高兴听到有关 BigQuery 或其他 SQL 的信息，因为我真的很好奇如何做到这一点。

Answer 1

这里有一点数学可以帮助 - 见下文

select *,
  ifnull(
    round(exp(sum(ln(debt)) over(order by id rows between unbounded preceding and current row))
    / exp(sum(ln(amount)) over(order by id rows between unbounded preceding and 1 preceding)), 2),
    amount
  ) cal
from `project.dataset.table`  

如果应用于您问题中的样本数据 - 输出是

注意：我使用order by id 假设id 列定义了行的顺序。您可以根据需要进行调整