一、建表语句
表名和字段
–1.学生表
Student(s_id,s_name,s_birth,s_sex) --学生编号,学生姓名, 出生年月,学生性别
–2.课程表
Course(c_id,c_name,t_id) – --课程编号, 课程名称, 教师编号
–3.教师表
Teacher(t_id,t_name) --教师编号,教师姓名
–4.成绩表
Score(s_id,c_id,s_score) --学生编号,课程编号,分数
--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`)
);
--教师表
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);
二、题目练习
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
stu.*, s.`s_score` as '01_score', c.`s_score` as '02_score'
from
`Student` AS stu
JOIN
`Score` AS s ON stu.`s_id` = s.`s_id` AND s.`c_id` = '01'
LEFT JOIN
`Score` as c ON stu.`s_id` = c.`s_id` AND c.`c_id` = '02'
WHERE
s.`s_score` > c.`s_score`;
2、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
stu.`s_id`, stu.`s_name`, ROUND(AVG(c.`s_score`), 2) as avg_score
from
`Student` as stu join `Score` as c on stu.`s_id` = c.`s_id`
GROUP BY
stu.`s_id`, stu.`s_name`
HAVING avg_score >= 60;
3、查询平均成绩小于60分的同学的学生编号和学生姓名和平均成绩
-- (包括有成绩的和无成绩的)
SELECT stu.`s_id`,
stu.`s_name`,
Round(Avg(c.`s_score`), 2) AS avg_score
FROM `Student` AS stu
JOIN `Score` AS c
ON stu.`s_id` = c.`s_id`
GROUP BY stu.`s_id`,
stu.`s_name`
HAVING avg_score < 60
UNION
SELECT `s_id`,
`s_name`,
0 AS avg_score
FROM `Student`
WHERE `s_id` NOT IN (SELECT DISTINCT `s_id`
FROM score);
4、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 stu.`s_id`,
stu.`s_name`,
Count(c.`c_id`) AS c_id,
Sum(c.`s_score`) AS sum_score
FROM `Student` AS stu
JOIN `Score` AS c
ON stu.`s_id` = c.`s_id`
GROUP BY stu.`s_id`,
stu.`s_name`
ORDER BY sum_score DESC;
5、查询姓李老师的数量
SELECT count(*) from `Teacher` WHERE `t_name` like '李%';
6、查询学过"张三"老师授课的同学的信息
SELECT *
FROM `Student` AS stu
LEFT JOIN `Score` AS c
ON stu.`s_id` = c.`s_id`
WHERE c.`c_id` IN (SELECT `c_id`
FROM `Course`
WHERE `t_id` IN (SELECT `t_id`
FROM `Teacher`
WHERE `t_name` = '张三'));
7、查询没学过"张三"老师授课的同学的信息
SELECT *
FROM `Student` AS stu
LEFT JOIN `Score` AS c
ON stu.`s_id` = c.`s_id`
WHERE c.`c_id` IN (SELECT `c_id`
FROM `Course`
WHERE `t_id` IN (SELECT `t_id`
FROM `Teacher`
WHERE `t_name` <> '张三'));
8、查询学过编号为"01"并且也学过编号为"02"的课程的同学的信息
SELECT *
FROM `Student` AS stu
JOIN `Score` AS c
ON stu.`s_id` = c.`s_id`
WHERE c.`c_id` = '01'
AND c.`c_id` = '02';
9、查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息
SELECT *
FROM `Student` AS stu
JOIN `Score` AS c
ON stu.`s_id` = c.`s_id`
WHERE c.`c_id` = '01'
AND c.`c_id` <> '02';
10、查询没有学全所有课程的同学的信息
SELECT *
FROM `Student` AS stu
WHERE stu.`s_id` IN (SELECT c.`s_id`
FROM `Score` AS c
GROUP BY c.`s_id`
HAVING Count(*) < (SELECT Count(DISTINCT `c_id`)
FROM `Course`))
11、查询至少有一门课与学号为"01"的同学所学相同的同学的信息
SELECT *
FROM `Student`,
`Score`
WHERE `Student`.`s_id` = `Score`.`s_id`
AND Score.`c_id` IN (SELECT c.`c_id`
FROM `Student` AS stu
JOIN `Score` AS c
ON stu.`s_id` = c.`s_id`
WHERE c.`s_id` = '01');
12、查询和"01"号的同学学习的课程完全相同的其他同学的信息
解法：
第一步：将01同学所学习的所有课程找出；
第二步：将01同学没学过的所有课程找出；
第三步：将学过01同学没学过的课程的同学找出，并排出；
第四步：统计剩余同学的课程数量如果和01同学的课程数量一致，则说明课程完全一致；
SELECT *
FROM `Student` AS stu
LEFT JOIN `Score` AS c
ON stu.`s_id` = c.`s_id`
WHERE c.`s_id` IN (SELECT `s_id`
FROM Score
GROUP BY `s_id`
HAVING Count(`s_id`) = (SELECT Count(DISTINCT `c_id`)
FROM Score
WHERE score.`s_id` = '01'))
AND c.`c_id` NOT IN (SELECT `c_id`
FROM `Score`
WHERE `c_id` NOT IN (SELECT `c_id`
FROM `Score`
WHERE `Score`.`s_id` = '01'));
13、查询没学过"张三"老师讲授的任一门课程的学生姓名
SELECT `Student`.`s_name`
FROM `Student`
WHERE `Student`.`s_id` NOT IN (SELECT `Score`.`s_id`
FROM `Score`
WHERE `Score`.`c_id` IN
(SELECT DISTINCT c.`c_id`
FROM `Teacher` AS t,
`Course` AS c
WHERE c.`t_id` = t.`t_id`
AND t.`t_name` = '张三')
);
