Trying to UNNEST timestamp array field, but need to GROUP BY - google-bigquery

Question

I have a repeated field of type TIMESTAMP in a BigQuery table. I am attempting to UNNEST this field. However, I must group or aggregate the field in order. I am not knowledgable with SQL, so I could use some help. The code snippet is part of a larger query that works when substituting subscription.future_renewal_dates with GENERATE_TIMESTAMP_ARRAY
subscription.future_renewal_dates is ARRAY<TIMESTAMP>
The TIMESTAMP array is unique (recurring subscriptions) and cannot be generated using GENERATE_TIMESTAMP_ARRAY, so I have to generate the dates before uploading to BigQuery. UDF is too much.
SELECT
subscription.amount AS subscription_amount,
subscription.status AS subscription_status,
"1" AS analytic_name,
ARRAY (
SELECT
AS STRUCT FORMAT_TIMESTAMP("%x", days) AS type_value, subscription.amount AS analytic_name
FROM
UNNEST(subscription.future_renewal_dates) as days
WHERE
(
days >= TIMESTAMP("2019-06-05T19:30:02+00:00")
AND days <= TIMESTAMP("2019-08-01T03:59:59+00:00")
)
) AS forecast
FROM
`mydataset.subscription` AS subscription
GROUP BY
subscription_amount,
subscription_status,
analytic_name
Cannot figure out how to successfully unnest subscription.future_renewal_dates without error 'UNNEST expression references subscription.future_renewal_dates which is neither grouped nor aggregated'

Answer 1

When you do GROUP BY - all expressions, columns in the SELECT (except those in GROUP BY list) should be used with some aggregation function - which you clearly do not have. So you need to decide what it is that you actually trying to achieve here with that grouping
Below is the option I think you had in mind - though it can be different - but at least you have an idea on how to fix it
SELECT
subscription.amount AS subscription_amount,
subscription.status AS subscription_status,
"1" AS analytic_name,
ARRAY_CONCAT_AGG( ARRAY (
SELECT
AS STRUCT FORMAT_TIMESTAMP("%x", days) AS type_value, subscription.amount AS analytic_name
FROM
UNNEST(subscription.future_renewal_dates) as days
WHERE
(
days >= TIMESTAMP("2019-06-05T19:30:02+00:00")
AND days <= TIMESTAMP("2019-08-01T03:59:59+00:00")
)
)) AS forecast
FROM
`mydataset.subscription` AS subscription
GROUP BY
subscription_amount,
subscription_status,
analytic_name