Show the customer id for all customers with an account.
select customer_id from accounts
Also show their first and last name.
select t1.customer_id, t2.customer_first_name, t2.customer_last_name from accounts as t1 join customers as t2 on t1.customer_id = t2.customer_id
Order them by the number of accounts in descending order.
select t1.customer_id, t2.customer_first_name, t2.customer_last_name from accounts as t1 join customers as t2 on t1.customer_id = t2.customer_id group by t1.customer_id order by count(*) desc
Who has the most?
select t1.customer_id, t2.customer_first_name, t2.customer_last_name from accounts as t1 join customers as t2 on t1.customer_id = t2.customer_id group by t1.customer_id order by count(*) desc limit 1