Context: CREATE TABLE Financial_transactions (card_id VARCHAR); CREATE TABLE Customers_cards (card_type_code VARCHAR, card_id VARCHAR)
Question: Show the card type codes and the number of transactions.
Answer: SELECT T2.card_type_code, COUNT(*) FROM Financial_transactions AS T1 JOIN Customers_cards AS T2 ON T1.card_id = T2.card_id GROUP BY T2.card_type_code