初学者问题，sql 语句写法和索引问题。

数据库中有五个表，分别是 a1,a2,a3,a4,a4,每个表中都有字段 banji,bainhao ,我想把这几个表关联起来
请问这样写对吗，或者有其他更好的写法，怎写执行速度能快

select * from a1 a
inner join a2 b on a.banji=b.banji
inner join a3 c on a.banji=c.banji
inner join a4 d on a.banji=d.banji
inner join a5 e on a.banji=e.banji
where a.bianhao=b.bianhao
and a.bianhao=c.bianhao
and a.bianhao=d.bianhao
and a.bianhao=e.bianhao

数据库中 表是否该建索引，或主键。这两个字段 banji,bainhao怎么建，建了查询速度能快吗。谢谢
[解决办法]
select * from a1 a
inner join a2 b on a.banji=b.banji
inner join a3 c on a.banji=c.banji
inner join a4 d on a.banji=d.banji
inner join a5 e on a.banji=e.banji

或者
select * from a1 a
, a2 b
, a3 c
, a4 d
, a5 e
where a.bianhao=b.bianhao
and a.bianhao=c.bianhao
and a.bianhao=d.bianhao
and a.bianhao=e.bianhao

[解决办法]
改成这样，更加清晰一点：

select * from a1 a 
inner join a2 b on a.banji=b.banji and a.bianhao=b.bianhao
inner join a3 c on a.banji=c.banji and a.bianhao=c.bianhao 
inner join a4 d on a.banji=d.banji and a.bianhao=d.bianhao
inner join a5 e on a.banji=e.banji and a.bianhao=e.bianhao 

[解决办法]
另外，可以建聚集索引，能加快速度：

create clustered index a1 on a1(banji,bianhao)

create clustered index a2 on a1(banji,bianhao)

create clustered index a3 on a1(banji,bianhao)

create clustered index a4 on a1(banji,bianhao)

create clustered index a5 on a1(banji,bianhao)
[解决办法]
看错了，要两个列的话用这种
select * from a1 a
inner join a2 b on a.banji=b.banji and a.bianhao=b.bianhao
inner join a3 c on a.banji=c.banji and a.bianhao=c.bianhao
inner join a4 d on a.banji=d.banji and a.bianhao=d.bianhao
inner join a5 e on a.banji=e.banji and a.bianhao=e.bianhao
或者：
select * from a1 a
, a2 b
, a3 c
, a4 d
,a5 e
where a.banji=e.banji and a.bianhao=e.bianhao and a.banji=d.banji and a.bianhao=d.bianhao and a.banji=c.banji and a.bianhao=c.bianhao and a.banji=b.banji and a.bianhao=b.bianhao

索引的话最好在关联条件的列上都加上。另外还要看你的结果是需要inner join还是left join