#1、从follow种找出user_id=1所关注的人 #2、从music_like种找出所关注人喜欢的音乐编号,去除出与1相同喜欢的相同编号的音乐 #3、查出为用户1所推荐的音乐 SELECT music_name from music where id in ( (SELECT music_id FROM music_likes where user_id IN (select follower_id from follow where user_id = 1) and music_id not in (SELECT music_id from music_likes where user...