Question: What percentage of orders were placed by customers in Madrid city in 1996?
SQL: 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