Write a query to find the customer balance summary (total, min, max, avg) for all customers who have not made purchases during the current invoicing period

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.