What is the difference of female and male audiences in number who viewed horror movies?
The audience and users are the same meaning; Difference of female and male audiences = count(female users) - count(male users); Female users refers to u_gender = 'F'; Male users refers to u_gender = 'M'
SELECT SUM(IIF(T2.u_gender = 'F', 1, 0)) - SUM(IIF(T2.u_gender = 'M', 1, 0)) FROM u2base AS T1 INNER JOIN users AS T2 ON T1.userid = T2.userid INNER JOIN movies2directors AS T3 ON T3.movieid = T1.movieid WHERE T3.genre = 'horror'