Pro Rata in BigQuery [duplicate] - sql

Question

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SQL equally distribute value by rows
(2 answers)
Do loop in BigQuery
(1 answer)
Closed 1 year ago.
I want to pro rate a table like this:
into a table like this:
essentially I want to create rows for the days between date_start and date end and then divide spend by how many days there are.
I am currently using the query below to do this, using BigQuery scripting - I know this probably is a horrible way of querying this but I'm not sure how else to do it. It takes about 30 seconds to run this query for just 3 rows.
DECLARE i INT64 DEFAULT 1;
DECLARE n int64;
SET n = (SELECT COUNT(*) FROM `pro_rata_test.data`);
DELETE FROM `pro_rata_test.pro_rata` WHERE TRUE;
WHILE i <= n DO
INSERT INTO
pro_rata_test.pro_rata
SELECT
day,
country,
campaign,
other,
SUM(spend)/(
SELECT
DATETIME_DIFF(DATETIME(TIMESTAMP(date_end)),
DATETIME(TIMESTAMP(date_start)),
DAY) + 1
FROM (
SELECT *, ROW_NUMBER() OVER(ORDER BY date_start) AS rn FROM `pro_rata_test.data`)
WHERE
rn = i) AS spend
FROM (
SELECT *, ROW_NUMBER() OVER(ORDER BY date_start) AS rn FROM `pro_rata_test.data`),
UNNEST(GENERATE_DATE_ARRAY(date_start, date_end)) day
WHERE
rn = i
GROUP BY
day,
country,
campaign,
other
ORDER BY
day;
SET
i = i + 1;
END WHILE

Answer 1

Try generate_date_array and unnest:
with mytable as (
select date '2021-01-01' as date_start, date '2021-01-10' as date_end, 100 as spend, 'FR' as country, 'Campaign1' as campaign, 'test1' as Other union all
select date '2021-01-11', date '2021-02-27', 150, 'UK', 'Campaign1', 'test2' union all
select date '2021-03-20', date '2021-04-20', 500, 'UK', 'Campaign2', 'test2'
)
select
day,
country,
campaign,
other,
spend/(date_diff(date_end, date_start, day)+1) as spend
from mytable, unnest(generate_date_array(date_start, date_end)) as day
order by day