Give counts of cities customers live in.
select t2.city, count(*) from customers as t1 join addresses as t2 on t1.customer_address_id = t2.address_id group by t2.city
Which city has most number of customers?
select t2.city from customers as t1 join addresses as t2 on t1.customer_address_id = t2.address_id group by t2.city order by count(*) desc limit 1;