What is the overall average amount of transactions?
select avg ( amount_of_transaction ) from transactions
How about average amount of transaction for different lots?
select t2.lot_id, avg ( amount_of_transaction ) from transactions as t1 join transactions_lots as t2 on t1.transaction_id = t2.transaction_id group by t2.lot_id
Which lot has the highest average transaction amount?
select t2.lot_id, avg ( amount_of_transaction ) from transactions as t1 join transactions_lots as t2 on t1.transaction_id = t2.transaction_id group by t2.lot_id order by avg ( amount_of_transaction ) desc limit 1
What about the lowest average?
select t2.lot_id, avg ( amount_of_transaction ) from transactions as t1 join transactions_lots as t2 on t1.transaction_id = t2.transaction_id group by t2.lot_id order by avg ( amount_of_transaction ) limit 1