Oracle中，考虑如下3个SQL： create view v1 as select department_id,department_name,last_name from departments join employees using (department_id); select department_name,last_name from v1 where department_id=20; select d.department_name,e.last_name from departments d, employees e where d.department_id=e.department_id and d.department_id=20; 关于第一个查询比第二个查询的说法正确的是？