mysql FROM多表时同时做为left join参数时报错

在查询的sql语句中，from两个表然后进行left join进行联查，原本想着根据from的两个表进行同时对left join中的信息进行筛选，却出现了错误信息

[Err] 1054 - Unknown column 'a' in 'on clause'

我的sql语句如下

select 
a.*,count(c.id) as number
from 
a,b
left join c on c.name = a.name 
and c.type = b.type
where ...
GROUP BY a.id

我要查询的是c表是与a和b表都有关联的，如果这样写就会报错，说是找不到a表的name数据
后来我把sql语句改成了下面这样就好了

select 
a.*,count(c.id) as number
from 
b
left join a on (这里随便来个判断即可)
left join c on c.name = a.name 
and c.type = b.type
where ...
GROUP BY a.id