这题不太好回，因为只要有连接，都有办法让它走hash join ,大不了强制hint 。
无论是基于RBO还是CBO，连接条件的本身都不是是否会走hash join的决定因素，比如下面这个例子

create table test_aa as select * from dba_objects;
create table test_bb as select * from dba_objects;

----hash join
select * from test_aa a, test_bb b where a.object_id = b.object_id ;
----hash join
select * from test_aa a, test_bb b where a.object_id = b.object_id and a.object_id=1;

create unique index xxxxxx on TEST_AA (object_id);

----hash join
select * from test_aa a, test_bb b where a.object_id = b.object_id ;
--NESTED LOOPS
select * from test_aa a, test_bb b where a.object_id = b.object_id and a.object_id=1;
复制

sql没变，就建了个索引，连接方式就变了；
而且同样的连接条件，只是过滤条件不一样，连接方式也可能会不一样；
甚至还有可能，连接条件和过滤条件一样，但由于表的数据量或返回的数据量不一样，采用的连接方式也会不一样。