Show the last name, id, and phone number for all customers.
select customer_last_name, customer_id, phone_number from customers
For each of them, show the number of orders as well.
select t2.customer_last_name, t1.customer_id, t2.phone_number, count(*) from orders as t1 join customers as t2 on t1.customer_id = t2.customer_id group by t1.customer_id
Sort them in descending order of the number of orders.
select t2.customer_last_name, t1.customer_id, t2.phone_number from orders 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 t2.customer_last_name, t1.customer_id, t2.phone_number from orders as t1 join customers as t2 on t1.customer_id = t2.customer_id group by t1.customer_id order by count(*) desc limit 1