Calculate the percentage of shipping done through Speedy Express.
through Speedy Express refers to CompanyName = 'Speedy Express'; percentage = divide(count(ShipperID where CompanyName = 'Speedy Express') , count(ShipperID)) * 100%
SELECT CAST(COUNT(CASE WHEN T2.CompanyName = 'Speedy Express' THEN 1 ELSE NULL END) AS REAL) * 100 / COUNT(T1.ShipVia) FROM Orders AS T1 INNER JOIN Shippers AS T2 ON T1.ShipVia = T2.ShipperID