How many payments are there in record?
select count(*) from payments
How many did each booking incur?
select booking_id, count(*) from payments group by booking_id
Which one has the largest number?
select booking_id from payments group by booking_id order by count(*) desc limit 1
Show me its id and the amount of refund.
select t1.booking_id, t1.amount_of_refund from bookings as t1 join payments as t2 on t1.booking_id = t2.booking_id group by t1.booking_id order by count(*) desc limit 1