CREATE TABLE invoices (billing_country VARCHAR, total INT)

A list of the top 10 countries by average invoice size. List country name and average invoice size.
SELECT billing_country, AVG(total) FROM invoices GROUP BY billing_country ORDER BY AVG(total) DESC LIMIT 10
SELECT "billing_country", AVG("total") FROM "invoices" GROUP BY "billing_country" ORDER BY AVG("total") DESC NULLS LAST LIMIT 10