Database: formula_1
Question: Among all European Grand Prix races, what is the percentage of the races were hosted in Germany?
SQL: SELECT CAST(COUNT(CASE WHEN T1.country = 'Germany' THEN T2.circuitID END) AS REAL) * 100 / COUNT(T2.circuitId) FROM circuits AS T1 INNER JOIN races AS T2 ON T2.circuitID = T1.circuitId WHERE T2.name = 'European Grand Prix'