原博客戳这里：点我跳转
(持续更新）

环境

• 1.MySQL 8.0
  -2. navicat for Mysql

建表

# 建表
# 学生表
CREATE TABLE `Student`(
    `s_id` VARCHAR(20),
    `s_name` VARCHAR(20) NOT NULL DEFAULT '',
    `s_birth` VARCHAR(20) NOT NULL DEFAULT '',
    `s_sex` VARCHAR(10) NOT NULL DEFAULT '',
    PRIMARY KEY(`s_id`)
);
# 课程表
CREATE TABLE `Course`(
    `c_id`  VARCHAR(20),
    `c_name` VARCHAR(20) NOT NULL DEFAULT '',
    `t_id` VARCHAR(20) NOT NULL,
    PRIMARY KEY(`c_id`)
);
# 师表
CREATE TABLE `Teacher`(
    `t_id` VARCHAR(20),
    `t_name` VARCHAR(20) NOT NULL DEFAULT '',
    PRIMARY KEY(`t_id`)
);
# 成绩表
CREATE TABLE `Score`(
    `s_id` VARCHAR(20),
    `c_id`  VARCHAR(20),
    `s_score` INT(3),
    PRIMARY KEY(`s_id`,`c_id`)
);
# 插入学生表测试数据
insert into Student values('01' , '赵雷' , '1990-01-01' , '男');
insert into Student values('02' , '钱电' , '1990-12-21' , '男');
insert into Student values('03' , '孙风' , '1990-05-20' , '男');
insert into Student values('04' , '李云' , '1990-08-06' , '男');
insert into Student values('05' , '周梅' , '1991-12-01' , '女');
insert into Student values('06' , '吴兰' , '1992-03-01' , '女');
insert into Student values('07' , '郑竹' , '1989-07-01' , '女');
insert into Student values('08' , '王菊' , '1990-01-20' , '女');
#课程表测试数据
insert into Course values('01' , '语文' , '02');
insert into Course values('02' , '数学' , '01');
insert into Course values('03' , '英语' , '03');

# 教师表测试数据
insert into Teacher values('01' , '张三');
insert into Teacher values('02' , '李四');
insert into Teacher values('03' , '王五');

#成绩表测试数据
insert into Score values('01' , '01' , 80);
insert into Score values('01' , '02' , 90);
insert into Score values('01' , '03' , 99);
insert into Score values('02' , '01' , 70);
insert into Score values('02' , '02' , 60);
insert into Score values('02' , '03' , 80);
insert into Score values('03' , '01' , 80);
insert into Score values('03' , '02' , 80);
insert into Score values('03' , '03' , 80);
insert into Score values('04' , '01' , 50);
insert into Score values('04' , '02' , 30);
insert into Score values('04' , '03' , 20);
insert into Score values('05' , '01' , 76);
insert into Score values('05' , '02' , 87);
insert into Score values('06' , '01' , 31);
insert into Score values('06' , '03' , 34);
insert into Score values('07' , '02' , 89);
insert into Score values('07' , '03' , 98);

对应的每个图如下：

1.course

course

2.score

score

3.student

student

4.teacher

teacher

习题

1.查询"01"课程比"02"课程成绩高的学生的信息及课程分数

SELECT a.*, b.s_score AS 01_score, c.s_score AS 02_score
FROM student a, score b, score c
WHERE a.s_id = b.s_id 
            AND a.s_id = c.s_id
            AND b.c_id = '01'
            AND c.c_id = '02'
            AND b.s_score > c.s_score;

2.查询"01"课程比"02"课程成绩低的学生的信息及课程分数

SELECT A.*, S1.s_score  AS 01_SCORE,S2.s_score AS 02_SCORE
FROM STUDENT A 
JOIN SCORE S1
ON A.s_id = S1.s_id AND S1.c_id = '01'
JOIN SCORE S2 
ON A.s_id = S2.s_id AND S2.c_id = '02'
WHERE S1.s_score < S2.s_score

3.查询平均成绩大于等于60分的同学的学生编号和学生姓名和平均成绩

SELECT S.s_id, S.s_name, AVG(A.s_score) AS AVG_SCORE
FROM STUDENT S 
JOIN SCORE A ON S.s_id = A.s_id
GROUP BY S.s_id
HAVING AVG_SCORE >= 60

5.查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩

SELECT S.s_id,S.s_name, COUNT(SC.c_id) AS courses, SUM(SC.s_score) AS total
FROM STUDENT S 
LEFT JOIN SCORE SC #这里需要左连接，因为不一定所有学生都选课了
ON S.s_id = SC.s_id
GROUP BY S.s_id , S.s_name

6.查询"李"姓老师的数量

SELECT COUNT(t_id) 
FROM TEACHER
WHERE t_name like '李%'