数据库创建外键的两种方式

create table dept(
    dId number,
    dName varchar2(20)
)

emptycreate table emp(
    eId number,
    constraint fk_depID FOREIGN KEY(eID) REFERENCES dept(dID)
)

create table emp(
eID number
);
alter table emp add constraint fk_depID FOREIGN KEY(eID) REFERENCES dept(dID);