orcal创建外键的几种方式

--表创建完成后添加外键

create table distict
(
       id number(4) primary key,
       name nvarchar2(20) not null
);


create table street
(
       id number(4) primary key,
       name nvarchar2(50) not null,
       district_id number(4)
);

alter table street add constraint distict_fk foreign key (district_id )  references distict (id);

--创建表的同时添加外键

create table distict
(
       id number(4) primary key,
       name nvarchar2(20) not null
);


create table street
(
       id number(4) primary key,
       name nvarchar2(50) not null,
       district_id number(4),

constraint distict_fk foreign key (district_id )  references distict (id)
);

--在字段属性中添加外键

create table distict
(
       id number(4) primary key,
       name nvarchar2(20) not null
);


create table street
(
       id number(4) primary key,
       name nvarchar2(50) not null,
       district_id references distict(id)
);