Write SQL query to solve given problem: Calculate the percentage of shipping done through Speedy Express.. Keep the solution inside sql tag ```sql [SQL-Query] ```
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