oracle left join测试

select * from 
test_users A,
test_hs B
where a.theme=b.username
and b.type='yy';

select * from 
test_users A,
test_hs B
where a.theme=b.username(+)
and b.type='yy';

select * from 
test_users A,
test_hs B
where a.theme=b.username(+)

select * from 
test_users A
left join test_hs B
on a.theme=b.username(+)
and b.type='yy';

select * from 
test_users A
left join test_hs B
on a.theme=b.username(+)
where b.type='yy';