What is the percentage of Japanese cars in the database?
Japanese car refers to country = 'Japan'; percentage = divide(count(ID where country = 'Japan'), count(ID)) * 100%
SELECT CAST(SUM(CASE WHEN T2.country = 'Japan' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(*) FROM production AS T1 INNER JOIN country AS T2 ON T1.country = T2.origin