Among the transactions, what percentage is done by using a visa card?
visa card refers to CreditCardType = 'Visa'; percentage = MULTIPLY(DIVIDE(SUM(CreditCardType = 'Visa'), COUNT(TransactionID)), 1.0);
SELECT CAST(COUNT(CASE WHEN CreditCardType = 'Visa' THEN TransactionID ELSE NULL END) AS REAL) * 100 / COUNT(TransactionID) FROM `transaction`