create table students( //创建students表 s_id int(10) primary key, //设置s_id为主键 s_name varchar(30) Not null, c_id varchar(30) Not null, s_gender varchar(30), s_score varchar(30) , foreign key (c_id) references classes (c_id)); //设置c_id为外键 create table classes( c_id varchar(30) primary key, c_name varchar(30), t_id int(10))