Top N items in every month - BIGQUERY - sql

Question

I have a big query program below;
WITH cte AS(
SELECT *
FROM (
SELECT project_name,
SUM(reward_value) AS total_reward_value,
DATE_TRUNC(date_signing, MONTH) as month,
date_signing,
Row_number() over (partition by DATE_TRUNC(date_signing, MONTH)
order by SUM(reward_value) desc) AS rank
FROM `deals`
WHERE CAST(date_signing as DATE) > '2019-12-31'
AND CAST(date_signing as DATE) < '2020-02-01'
AND target_category = 'achieved'
AND project_name IS NOT NULL
GROUP BY project_name, month, date_signing
)
)
SELECT * FROM cte WHERE rank <= 5
that returns the following result:
While I expect to have each unique project to be SUM within each month and then I filter only the top 5.
Something like this:
I got the following error if the date_signing grouping is removed
PARTITION BY expression references column date_signing which is neither grouped nor aggregated at [16:48]
Any hints what should be corrected will be appreciated!

Answer 1

One more subquery maybe then?
WITH cte AS(
SELECT project_name,
SUM(reward_value) as reward_sum,
DATE_TRUNC(date_signing, MONTH) as month
FROM `deals`
WHERE CAST(date_signing as DATE) > '2019-12-31'
AND CAST(date_signing as DATE) < '2020-02-01'
AND target_category = 'achieved'
AND project_name IS NOT NULL
GROUP BY project_name, month
),
ranks AS (
SELECT
project_name,
reward_sum,
month,
ROW_NUMBER() over (PARTITION BY month ORDER BY reward_sum DESC) AS rank
)
SELECT *
FROM ranks
WHERE rank <= 5

Answer 2

yeah you can't do that , yo can show the last signing date instead:
WITH cte AS(
SELECT project_name,
SUM(reward_value),
DATE_TRUNC(date_signing, MONTH) as month,
MAX(date_signing) as last_signing_date,
Row_number() over (partition by DATE_TRUNC(date_signing, MONTH)
order by SUM(reward_value) desc) AS rank
FROM `deals`
WHERE CAST(date_signing as DATE) > '2019-12-31'
AND CAST(date_signing as DATE) < '2020-02-01'
AND target_category = 'achieved'
AND project_name IS NOT NULL
GROUP BY project_name, month
)
SELECT * FROM cte WHERE rank <= 5