Please show the description of the transaction type "SALE".
select transaction_type_description from ref_transaction_types where transaction_type_code = "SALE"
How many transaction types are there?
select count(*) from ref_transaction_types
Among these transactions, which one occurs most frequently?
select t1.transaction_type_code from ref_transaction_types as t1 join transactions as t2 on t1.transaction_type_code = t2.transaction_type_code group by t1.transaction_type_code order by count(*) desc limit 1
Show its description.
select t1.transaction_type_description from ref_transaction_types as t1 join transactions as t2 on t1.transaction_type_code = t2.transaction_type_code group by t1.transaction_type_code order by count(*) desc limit 1