表的关联查询，哪种写法效率更高？

方法1：嵌套子查询

select col1,col2 
from tab1
where id in (select 2_id 
      from tab2
      where order_num in ( select order_num 
                     from  tab3
                     where prod_id='AAA'))

方法2：无嵌套子查询

select col1,col2 
from tab1,tab2,tab3
where 
tab1.id=tab2.id
and tab2.order_num =tab3.order_num 
and tab3.prod_id='AAA'

方法3：INNER JOIN

select col1,col2 
from tab1
inner join tab2 on tab1.id=tab2.id
inner join tab3 on tab2.order_num =tab3.order_num 
where 
prod_id='AAA'

我估计不同的数据库的优化器，性能应该是有千差万别的。

请各位在不同的数据库上进行测试，并帮忙反馈一下测试结果哟