This (dialect agnostic) example handles a single invoice with multiple items and different prices and quantities per item. To compute an average per customer, you first want to sum within each invoice.
Select the columns:
bipp generates the SQL:
SELECT t000.customer_id AS _0, avg(t001.transaction_amount) AS _1 FROM `online_retail`.`transactions` AS t000 JOIN ( SELECT transactions.invoice_num AS invoice_num, sum(transactions.invoice_qnty * transactions.unit_price) AS transaction_amount FROM `online_retail`.`transactions` AS transactions GROUP BY invoice_num) AS t001 ON t000.invoice_num=t001.invoice_num GROUP BY 1
Fetch the data:
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