What percentage of orders were placed by customers in Madrid city in 1996?
"Madrid" is the City; in 1996 refers to YEAR (OrderDate) = 1996; percentage = Divide (Count (CustomerID where City = 'Madrid'), Count (CustomerID)) * 100
SELECT CAST(COUNT(CASE WHEN T1.City = 'Madrid' THEN 1 ELSE NULL END) AS REAL) * 100 / COUNT(T1.City) FROM Customers AS T1 INNER JOIN Orders AS T2 ON T1.CustomerID = T2.CustomerID WHERE STRFTIME('%Y', T2.OrderDate) = 1996