CREATE TABLE volume (volume_id DECIMAL, volume_issue TEXT, issue_date TEXT, weeks_on_top DECIMAL, song TEXT, artist_id DECIMAL)
CREATE TABLE artist (artist_id DECIMAL, artist TEXT, age DECIMAL, famous_title TEXT, famous_release_date TEXT)
CREATE TABLE music_festival (id DECIMAL, music_festival TEXT, date_of_ceremony TEXT, category TEXT, volume DECIMAL, result TEXT)

What are the categories of music festivals for which there have been more than 1 music festival?
SELECT category FROM music_festival GROUP BY category HAVING COUNT(*) > 1
SELECT "category" FROM "music_festival" GROUP BY "category" HAVING COUNT(*) > 1