Answer:
SELECT SUM(customer_balance) as Total, MIN(customer_balance) as minimum_balance, Max(customer_balance) as maximum_balance, AVG(customer_balance) as average_balance FROM customers WHERE customer_id NOT IN (SELECT customer_id FROM invoice)
Explanation:
The SQL query statement returns four columns which are aggregates of the column customer_balance from the customers table in the database and the rows are for customers that have not made any purchase during the current invoicing period.
