Show the amount of transactions whose type code is "PUR"
select amount_of_transaction from transactions where transaction_type_code = "PUR"
Show average amount of transactions whose type code is "PUR"
select avg(amount_of_transaction) from transactions where transaction_type_code = "PUR"
Show the minimum amount of transactions whose type code is "PUR" and whose share count is bigger than 50.
select min(amount_of_transaction) from transactions where transaction_type_code = "PUR" and share_count > 50