How to pluck the oldest child record from a join in BigQuery SQL where ordered by date and limit 1 - google-cloud-platform

Question

I'm analyzing Shopify Schema Data with BiqQuery in GCP and trying to join the Shopify Customers data to the child record that is Orders data so that I can find the very first Order for each Customer created in a certain time, but limit that to 1...like order by created_at asc, limit 1. I'm not really able to figure this out
Select
customers.created_at as customer,
customers.orders_count,
orders.created_at,
orders.order_number
FROM `shopxxx.shopify.customers` as customers
Join `shopxxx.shopify.orders` as orders
on customer = orders.customer
WHERE
customers.orders_count != 0
AND customers.created_at > "2018-09-12 00:00:00 UTC" and customers.created_at < "2019-09-12 23:59:59 UTC"
and orders.source_name != 'web'
order by customers.created_at desc

Answer 1

Below is for BigQuery Standard SQL
#standardSQL
SELECT
customers.customer_id,
customers.created_at AS customer,
customers.orders_count,
ARRAY_AGG(STRUCT(orders.created_at AS created_at, orders.order_number AS order_number) ORDER BY orders.created_at LIMIT 1)[OFFSET(0)].*
FROM `shopxxx.shopify.customers` AS customers
JOIN `shopxxx.shopify.orders` AS orders
ON customers.customer_id = orders.customer_id
WHERE customers.orders_count != 0
AND customers.created_at > "2018-09-12 00:00:00 UTC" AND customers.created_at < "2019-09-12 23:59:59 UTC"
AND orders.source_name != 'web'
GROUP BY 1, 2, 3
ORDER BY customers.created_at DESC
or different approach
#standardSQL
SELECT
customers.customer_id,
customers.created_at AS customer,
customers.orders_count,
orders.created_at AS created_at,
orders.order_number AS order_number
FROM `shopxxx.shopify.customers` AS customers
JOIN (
SELECT customer_id, ARRAY_AGG(STRUCT(created_at, order_number) ORDER BY created_at LIMIT 1)[OFFSET(0)].*
FROM `shopxxx.shopify.orders`
WHERE source_name != 'web' GROUP BY customer_id
) AS orders
ON customers.customer_id = orders.customer_id
WHERE customers.orders_count != 0
AND customers.created_at > "2018-09-12 00:00:00 UTC" AND customers.created_at < "2019-09-12 23:59:59 UTC"
ORDER BY customers.created_at DESC