1、创建数据库test
2、创建学生表student1

(sid,sname,sage,ssex) Sid学号 ,sname学生姓名，sage学生年龄，ssex学生性并指定值为男或女 设置默认值为男 Sid为主键自增，sname设置为唯一

-- CREATE DATABASE test;
USE test;
CREATE TABLE student1(
sid INT primary key auto_increment,
sname char(10) unique,
sage INT,
ssex enum('女','男') not null default '男'
)charset='utf8';

#添加charset='utf8'是因为ssex中的中文字符无法识别，会报错

3、创建课程表course(cid,cname,tid) cid为主键自增

CREATE TABLE course(
cid INT PRIMARY KEY auto_increment,
cname CHAR(10),
tid INT
);

 4、创建成绩表cj(sid,cid,score)sid,cid为外键字段，依次关联学生表和课程表

    CREATE TABLE score(
    score INT PRIMARY KEY auto_increment
    stu_sid INT,
    FOREIGN key(stu_sid) REFERENCES student(sid),
    cour_cid INT,
    FOREIGN key(cour_cid) REFERENCES course(cid)
    );

5、教师表：t(tid,sname)    tid教师编号为主键，tname教师名字

 CREATE TABLE teacher( tid INT PRIMARY key, sname CHAR(10) ); 

6、学生表中插入数据

INSERT INTO student1(sname,sage) VALUES('张三',16);
INSERT INTO student1(sname,sage) VALUES('李四',15);
INSERT INTO student1(sname,sage) VALUES('王五',16);
INSERT INTO student1(sname,sage) VALUES('马六',17);
INSERT INTO student1(sname,sage) VALUES('陈七',14);

7、教师表中插入数据

INSERT INTO teacher(tid,sname) VALUES(1,'包包');
INSERT INTO teacher(tid,sname) VALUES(2,'老向');
INSERT INTO teacher(tid,sname) VALUES(3,'老张');
INSERT INTO teacher(tid,sname) VALUES(4,'春哥');

8、课程表中插入数据

INSERT INTO course(cid,cname,tid) VALUES(1,'语文',1);
INSERT INTO course(cid,cname,tid) VALUES(2,'数学',2);
INSERT INTO course(cid,cname,tid) VALUES(3,'英语',3);
INSERT INTO course(cid,cname,tid) VALUES(4,'日语',4);

9、成绩表中插入数据

INSERT INTO cj(sid,cid,score) VALUES(1,1,30);
INSERT INTO cj(sid,cid,score) VALUES(1,2,60);
INSERT INTO cj(sid,cid,score) VALUES(1,3,70);
INSERT INTO cj(sid,cid,score) VALUES(2,1,60);
INSERT INTO cj(sid,cid,score) VALUES(2,2,70);
INSERT INTO cj(sid,cid,score) VALUES(3,2,30);
INSERT INTO cj(sid,cid,score) VALUES(3,3,80);
INSERT INTO cj(sid,cid,score) VALUES(4,1,70);
INSERT INTO cj(sid,cid,score) VALUES(4,2,60);
INSERT INTO cj(sid,cid,score) VALUES(4,3,80);
INSERT INTO cj(sid,cid,score) VALUES(4,4,90);
INSERT INTO cj(sid,cid,score) VALUES(5,1,90);
INSERT INTO cj(sid,cid,score) VALUES(5,4,90);

10、修改教师表的sname为tname,并且数据类型设置为varchar2(20),删除学生表SSEX字段

ALTER TABLE teacher CHANGE sname tname VARCHAR(20)

ALTER TABLE student1 DROP ssex 

11、修改张三的语文成绩为80分

UPDATE cj SET score=80 WHERE sid=1 and cid=1

12、插入一条数据到cj，插入的数据如下(1,4,90)

 INSERT INTO cj(sid,cid,score) VALUES(1,4,90);  

13、删除陈七日语成绩

 DELETE FROM cj WHERE sid=5 AND cid=4 

14、查询（一条一个查询）

select * from student1; 

select sid from student1; 

SELECT * FROM student1 WHERE sage LIKE '%6%'

SELECT * FROM student1 WHERE sage BETWEEN 14 AND 16

SELECT * FROM student1 WHERE sage IN(1,14,15)

SELECT * FROM student1 WHERE sage is NULL

SELECT * FROM student1 WHERE sage is not NULL

SELECT * FROM student1 WHERE sage NOT IN(14,15)