请写出计算粉丝ctr的sql语句

drop table if exists a;
create table `a` (
author_id varchar(32) not null,
fans_id varchar(32) not null,
create_date varchar(32) not null
);
insert into a values ('332579','985035','2022/1/1');
insert into a values ('332579','849602','2022/1/15');
insert into a values ('332579','952566','2022/3/20');
insert into a values ('970382','930554','2022/6/1');
insert into a values ('970382','985035','2022/9/23');
insert into a values ('960725','590742','2022/11/10');
insert into a values ('960725','985035','2022/12/6');
insert into a values ('960725','940672','2023/1/12');
insert into a values ('960725','392056','2023/2/10');


drop table if exists b;
create table `b` (
author_id varchar(32) not null,
content_id varchar(32) not null
);
insert into b values ('332579','790046624');
insert into b values ('332579','391056935');
insert into b values ('970382','486962456');
insert into b values ('970382','359325633');
insert into b values ('970382','899054463');
insert into b values ('960725','125225355');
insert into b values ('490626','738258392');
insert into b values ('490626','678329246');
insert into b values ('230563','239587593');


drop table if exists c;
create table `c` (
content_id varchar(32) not null,
fans_id varchar(32) not null,
show_num int not null,
read_num int not null,
like_num int not null,
comment_num int not null
);
insert into c values ('790046624','985035',1,1,0,0);
insert into c values ('790046624','583951',1,1,0,0);
insert into c values ('391056935','123573',1,1,0,1);
insert into c values ('391056935','395621',1,1,0,1);
insert into c values ('391056935','985035',2,1,0,1);
insert into c values ('486962456','985035',1,1,1,1);
insert into c values ('486962456','838495',1,1,1,1);
insert into c values ('359325633','952566',2,0,0,0);
insert into c values ('899054463','952566',1,0,0,0);
insert into c values ('125225355','985035',1,1,1,0);

fans_ctr
0.8000