对于非空外键,左外连接等同于内连接吗?

每个城市都有自己的国家:

create table COUNTRY 
(
     ID number not null,
     NAME varchar,
     primary key (ID)
);

create table CITY 
(
     ID number not null,
     NAME varchar,
     COUNTRY_ID number not null,
     primary key (ID)
);

alter table CITY 
    add constraint CITY_COUNTRY_FK
        foreign key (COUNTRY_ID) references COUNTRY (ID);

详情如下:

select * 
from CITY c
left outer join COUNTRY ctr on ctr.ID = c.COUNTRY_ID
where ...;

相当于:

select * 
from CITY c
inner join COUNTRY ctr on ctr.ID = c.COUNTRY_ID
where ...;

因为国家ID是 foreign key 和 not null ?