题解 | 请写出计算粉丝ctr的sql语句

select
    sum(h1.read_num) / sum(h1.show_num) as fans_ctr
from
    (
        select
            c.content_id,
            fans_id,
            show_num,
            read_num,
            author_id
        from
            c
            left outer join b on c.content_id = b.content_id
    ) as h1
    right outer join a on h1.fans_id = a.fans_id
    and h1.author_id = a.author_id