1.商品表
create table product( pid varchar(32) primary key, pname varchar(40), price double, category_id varchar(32) );
2.订单表
create table orders( oid varchar(32) primary key, totalprice double );
3.订单项表
create table orderitem( oid varchar(50), pid varchar(50) );
4.订单表和订单项表的主外键关系
alter table orderitem add constraint orderitem_orders_fk foreign key(oid) references orders(oid);
5.商品表和订单项表的主外键关系
alter table orderitem add constraint orderitem_product_fk foreign key(pid) references product(pid);