Question: Calculate the percentage of directors whose films grossed over $100 million.
SQL: SELECT CAST(COUNT(DISTINCT CASE WHEN CAST(REPLACE(trim(T1.total_gross, '$'), ',', '') AS REAL) > 100000000 THEN T3.director ELSE NULL END) AS REAL) * 100 / COUNT(DISTINCT T3.director) FROM movies_total_gross AS T1 INNER JOIN characters AS T2 ON T1.movie_title = T2.movie_title INNER JOIN director AS T3 ON T1.movie_title = T3.name