--试试这个
select t1.name,t2.b_name,busi_id数量=(select count(busi_id) from c where c_id=t3.c_id) from c t3
left join a t1 on t1.a_id=t3.a_id
left join b t2 on t2.b_id=t3.b_id

------解决方案--------------------

1.这个数据库的表设计有问题,a是b 的父,b是c的父,可是a又是c的父,这种结构必须保证数据不能有交叉,如果有交叉,父子关系便出错了.
2.楼主的需求描述不太清楚,你倒底是要输出全部信息,还是输出统计信息?

做了个例子,可以实现,程序应该可以在MYSQL 里运行,但不敢保证适合你的需求.

SQL code
create table a(a_id int,name varchar(10))
create table b(b_id int,a_id int,b_name varchar(10))
create table c(busi_id int,a_id int,b_id int)
insert into a select 1,'aa'
insert into a select 2,'bb'
insert into b select 1,1,'afds'
insert into b select 2,1,'awef'
insert into b select 3,2,'vais'
insert into c select 51,1,2
insert into c select 13,1,1
--insert into c select 38,2,2  --这样的记录是有问题的
go
select a.name,b.b_name,c.busi_id,
(select count(*) from c t where t.a_id=a.a_id and t.b_id=b.b_id)ct
from a left join b on a.a_id=b.a_id
left join c on c.a_id=a.a_id and c.b_id=b.b_id
/*
name       b_name     busi_id     ct
---------- ---------- ----------- -----------
aa         afds       13          1
aa         awef       51          1
bb         vais       NULL        0

(3 行受影响)

*/
go
drop table a,b,c

------解决方案--------------------
SQL code
--修改
select
   a.name,b.b_name,c.num
from
   a left join b
on
   a.a_id=b.a_id
left join
   (select  busi_id,a_id,b_id,count(1) as num from c group by a_id,b_id,busi_id)c
on
   c.a_id=a.a_id and c.b_id=b.b_id