Show the description of the transaction type that occurs most frequently.
create table transactions (transaction_type_code varchar, PRIMARY KEY (transaction_type_code)); create table ref_transaction_types (transaction_type_description varchar, transaction_type_code varchar, PRIMARY KEY (transaction_type_description))
select t1.transaction_type_code, 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, t1.transaction_type_description order by count(*) desc limit 1;