创建一个名为course的数据库 在该数据库下创建以下几个表： Students表：sid整型自增主键，sname字符串64位，gender字符串12位，dept_id整型并外键到dept表的id字段 Dept表：id整型自增主键，dept_name字符串64位 Course表：id整型自增字段主键，course_name字符串64位，teacher_id整型外键到teacher表的id字段 Teacher表：id整型自增字段主键，name字符串64位，dept_id整型外键到dept表的id字段 创建选课成绩表score(sid,course_id,score) **Students表和teacher表的dept_id为非空** ~~~ create database course; use course; create table dept( id int auto_increment primary key, dept_name varchar(64) ); create table students( sid int auto_increment primary key, sname varchar(64), gender varchar(12), dept_id int not null , constraint for_1 foreign key(dept_id) references dept(id) ); create table teacher (id int auto_increment primary key, name varchar(64), dept_id int not null, constraint for_3 foreign key(dept_id) references dept(id) ); create table course ( id int auto_increment primary key, course_name varchar(64), teacher_id int, constraint for_2 foreign key(teacher_id) references teacher(id) ); create table score(sid int,course_id int,score int); ~~~