oracle 创建表 外键约束

 create table usertable(
        id int primary key,
        username varchar(32) not null,
        birthday date,
        sex char(1),
        address varchar(256)
 );

create table orders(
       id int primary key,
       user_id int not null,
       numberid varchar(32) not null,
       createtime date,
       note varchar(100),
       constraint fk_orders foreign key (user_id) references usertable(id)
);