BQ: How to UNNEST into new table - google-maps

Question

I'm exporting billing data from Google Cloud Platform to BigQuery (BQ).
The task at hand is to build a query that UNNEST relevant data to a new 'flat' table
The structure of the data in BQ is this:
[{
"billing_account_id": "01234-1778EC-123456",
"service": {
"id": "2062-016F-44A2",
"description": "Maps"
},
"sku": {
"id": "5D8F-0D17-AAA2",
"description": "Google Maps"
},
"usage_start_time": "2018-11-05 14:45:00 UTC",
"usage_end_time": "2018-11-05 15:00:00 UTC",
"project": {
"id": null,
"name": null,
"labels": []
},
"labels": [],
"system_labels": [],
"location": null,
"export_time": "2018-11-05 21:54:09.779 UTC",
"cost": "5.0",
"currency": "EUR",
"currency_conversion_rate": "0.87860000000017424",
"usage": {
"amount": "900.0",
"unit": "seconds",
"amount_in_pricing_units": "0.00034674063800277393",
"pricing_unit": "month"
},
"credits": "-1.25",
"invoice": {
"month": "201811"
}
},
I wish to schedule a job that builds a new table every day with just this schema
billing_account_id, usage_start_time, usage_end_time, cost, credit_amount
So far I'm at this:
select billing_account_id, usage_start_time, usage_end_time, cost, credits AS CREDITS from clientBilling.gcp_billing_export_v1_XXXX , UNNEST(credits);
But in the results credits are still nested and not 'flat' as I need. Any input is welcome, thanks! :)
Result

Answer 1

credits is an array of structs (each struct being "name, amount") - a "repeated" record in BigQuery - so you have to first unnest the array and then reference the struct member you want.
Thus:
UNNEST the credits record
Alias the credits.amount struct member as credit_amount
SELECT
billing_account_id,
usage_start_time,
usage_end_time,
cost,
credit.amount as credit_amount
FROM
`optimum-rock-145719.billing_export.gcp_billing_export_v1*`,
UNNEST(credits) as credit
This will return a result table with just the credits.amount column as credits_amount. You were doing step 1, but not step 2, and ignoring the unnested fields in your SELECT clause.