Database: social_media
Question: What is the percentage of the tweets from California are positive?
SQL: SELECT SUM(CASE WHEN T1.Sentiment > 0 THEN 1.0 ELSE 0 END) / COUNT(T1.TweetID) AS percentage FROM twitter AS T1 INNER JOIN location AS T2 ON T2.LocationID = T1.LocationID WHERE State = 'California'