Recursive calculation in BigQuery [duplicate] - google-bigquery

Question

This question already has an answer here:
It's possible to create a rule in preceding rows in sum?
(1 answer)
Closed 2 years ago.
I need to calculate stock as a dinamic and recursive value, as the simple equation:
n value refers to a periodic time (month, day, year, etc)
Always when a stock value is negative, this is replaced by zero.
How can I calculate this in Big Query? Here is a example:
WITH `project.dataset.table` AS (
SELECT 10 entrada, 5 venda, 8 quebra, 8 mes, 2019 ano UNION ALL
SELECT 12, 8 , 3, 9, 2019 UNION ALL
SELECT 20, 15, 2, 10, 2019 UNION ALL
SELECT 30, 12, 2, 11, 2019 UNION ALL
SELECT 20, 10, 5, 12, 2019 UNION ALL
SELECT 30, 12, 2, 1, 2020 UNION ALL
SELECT 30, 12, 2, 2, 2020 UNION ALL
SELECT 30, 12, 2, 3, 2020
)
SELECT entrada, venda, quebra,
variacao,
greatest(coalesce(lag(variacao) over (partition by 'project.dataset.table' order by ano, mes),0) + entrada - venda - quebra, 0) as estoque
FROM (
SELECT *,
entrada - venda - quebra AS variacao
FROM `project.dataset.table`
)
And the expected result would be:
entrada venda quebra variacao estoque
10 5 8 -3 0
12 8 3 1 1
20 15 2 3 4
30 12 2 16 20
20 10 5 5 25
30 12 2 16 41
30 12 2 16 57
30 12 2 16 73
But, the results for the code above is:
entrada venda quebra variacao estoque
10 5 8 -3 0
12 8 3 1 0
20 15 2 3 4
30 12 2 16 19
20 10 5 5 21
30 12 2 16 21
30 12 2 16 32
30 12 2 16 32
Thanks in advance!

Answer 1

BigQuery does not support recursive operations natively. Try array_agg() combined with JavaScript user-defined function, but this approach is not very scalable:
CREATE TEMP FUNCTION special_sum(x ARRAY<INT64>)
RETURNS INT64
LANGUAGE js
AS """
var estoque = 0;
for (const num of x)
{
estoque = Math.max(estoque + parseInt(num), 0);
}
return estoque;
""";
WITH `project.dataset.table` AS (
SELECT 10 entrada, 5 venda, 8 quebra, 8 mes, 2019 ano UNION ALL
SELECT 12, 8 , 3, 9, 2019 UNION ALL
SELECT 20, 15, 2, 10, 2019 UNION ALL
SELECT 30, 12, 2, 11, 2019 UNION ALL
SELECT 20, 10, 5, 12, 2019 UNION ALL
SELECT 30, 12, 2, 1, 2020 UNION ALL
SELECT 30, 12, 2, 2, 2020 UNION ALL
SELECT 30, 12, 2, 3, 2020
)
select *,
special_sum(array_agg(entrada - venda - quebra) over (order by ano, mes rows unbounded preceding)) as estoque
from `project.dataset.table`

Answer 2

Solved using a "internal" sum of all values of stock. Using this:
WITH `project.dataset.table` AS (
SELECT 10 entrada, 5 venda, 8 quebra, 8 mes, 2019 ano UNION ALL
SELECT 12, 8 , 3, 9, 2019 UNION ALL
SELECT 20, 15, 2, 10, 2019 UNION ALL
SELECT 30, 12, 2, 11, 2019 UNION ALL
SELECT 20, 10, 5, 12, 2019 UNION ALL
SELECT 30, 12, 2, 1, 2020 UNION ALL
SELECT 30, 12, 2, 2, 2020 UNION ALL
SELECT 30, 12, 2, 3, 2020
)
SELECT entrada, venda, quebra,
sum(greatest(entrada - venda - quebra,0)) over (partition by 'project.dataset.table' order by ano, mes) as estoque,
mes, ano
FROM `project.dataset.table`