Can you show me the total invoice size per country!
select billing_country, sum(total) from invoices group by billing_country;
Instead, display the average per country!
select billing_country, avg(total) from invoices group by billing_country;
Just, show the top 15 by average invoice size.
select billing_country, avg(total) from invoices group by billing_country order by avg(total) desc limit 15;
Actually, just list the top 10!
select billing_country, avg(total) from invoices group by billing_country order by avg(total) desc limit 10;