Question: Of the arts-books and arts-design categories, which one has more podcasts and what is the numerical difference between them?
SQL: SELECT ( SELECT category FROM categories WHERE category = 'arts-books' OR category = 'arts-design' GROUP BY category ORDER BY COUNT(podcast_id) DESC LIMIT 1 ) "has more podcasts" , ( SELECT SUM(CASE WHEN category = 'arts-books' THEN 1 ELSE 0 END) - SUM(CASE WHEN category = 'arts-design' THEN 1 ELSE 0 END) FROM categories ) "differenct BETWEEN arts-books and arts-design"