Database: law_episode
Question: How many episodes are there in the 9th season of Law and Order? Calculate the average number of casts per season of the said series.
SQL: SELECT SUM(CASE WHEN T2.season = 9 THEN 1 ELSE 0 END) AS num , CAST(SUM(CASE WHEN T2.season = 9 THEN 1 ELSE 0 END) AS REAL) / COUNT(T1.episode_id) FROM Credit AS T1 INNER JOIN Episode AS T2 ON T1.episode_id = T2.episode_id WHERE T1.category = 'Cast' AND T2.series = 'Law and Order'