Question

sql 设置主外键关系语句

谁能给我写一个主外键关系的语句，或者用alter修改成主外键关系的语句,谢谢了！

Answer 1

--表tb_user
create table tb_user (
id int not null,
username varchar(32) not null
);
--给tb_user添加主键
alter table tb_user add constraint pk_users primary key (id);

--表tb_course
create table tb_course (
id int not null primary key,
name varchar(20) not null
);

--表tb_mark
create table tb_mark (
uid int not null,
cid int not null,
mark int not null,
primary key (uid, cid)
);
--给tb_mark添加外键
alter table tb_mark add constraint fk_uid foreign key(uid) references tb_user(id);
alter table tb_mark add constraint fk_cid foreign key(cid) references tb_course(id);