MySQL多表关联查询练习

创建表student和score

CREATE  TABLE student (
id  INT(10)  NOT NULL  UNIQUE  PRIMARY KEY ,
`name`  VARCHAR(20)  NOT NULL ,
sex  VARCHAR(4) ,
birth  YEAR,
department  VARCHAR(20) ,
address  VARCHAR(50)
);
    
CREATE  TABLE score (
id  INT(10)  NOT NULL  UNIQUE  PRIMARY KEY  AUTO_INCREMENT ,
stu_id  INT(10)  NOT NULL ,
c_name  VARCHAR(20) ,
grade  INT(10)
);

INSERT INTO student VALUES( 901,'张老大', '男',1985,'计算机系','北京市海淀区');
INSERT INTO student VALUES( 902,'张老二', '男',1986,'中文系', '北京市昌平区');
INSERT INTO student VALUES( 903,'张三', '女',1990,'中文系', '湖南省永州市');
INSERT INTO student VALUES( 904,'李四', '男',1990,'英语系', '辽宁省阜新市');
INSERT INTO student VALUES( 905,'王五', '女',1991,'英语系', '福建省厦门市');
INSERT INTO student VALUES( 906,'王六', '男',1988,'计算机系', '湖南省衡阳市');

INSERT INTO score VALUES(NULL,901, '计算机',98);
INSERT INTO score VALUES(NULL,901, '英语', 80);
INSERT INTO score VALUES(NULL,902, '计算机',65);
INSERT INTO score VALUES(NULL,902, '中文',88);
INSERT INTO score VALUES(NULL,903, '中文',95);
INSERT INTO score VALUES(NULL,904, '计算机',70);
INSERT INTO score VALUES(NULL,904, '英语',92);
INSERT INTO score VALUES(NULL,905, '英语',94);
INSERT INTO score VALUES(NULL,906, '计算机',90);
INSERT INTO score VALUES(NULL,906, '英语',85);

#查询：
#查询student表的所有记录
SELECT * 
FROM student;

#查询student表的第2条到4条记录
SELECT * 
FROM student 
WHERE id 
BETWEEN 902 AND 904;

#从student表查询所有学生的学号（id）、姓名（name）和院系（department）的信息
SELECT id, `name`, department 
FROM student; 

#从student表中查询计算机系和英语系的学生的信息
SELECT * 
FROM student 
WHERE department IN ('计算机系', '英语系');

#从student表中查询年龄28~32岁的学生信息
SELECT * 
FROM student 
WHERE (2020 - birth) 
BETWEEN 28 AND 32;

、

#从student表中查询每个院系有多少人
SELECT department, COUNT(*) 
FROM student 
GROUP BY (department);

#从score表中查询每个科目的最高分
SELECT c_name, MAX(grade) 
FROM score 
GROUP BY (c_name);

#查询李四的考试科目（c_name）和考试成绩（grade）
SELECT student.name, score.c_name, score.grade 
FROM score, student 
WHERE student.id = score.stu_id 
AND student.name = '李四';

#用连接的方式查询所有学生的信息和考试信息
SELECT * 
FROM score, student 
WHERE student.id = score.stu_id;

#计算每个学生的总成绩
SELECT student.name, SUM(grade) 
FROM score, student 
WHERE student.id = score.stu_id 
GROUP BY (score.stu_id);

#计算每个考试科目的平均成绩
SELECT c_name, AVG(grade) 
FROM score 
GROUP BY (c_name);

#查询计算机成绩低于95的学生信息
SELECT student.* 
FROM score, student 
WHERE student.id = score.stu_id 
AND score.c_name = '计算机' 
AND grade < 95;

#查询同时参加计算机和英语考试的学生的信息
SELECT s.* 
FROM student AS s, score AS s1, score AS s2 
WHERE s.id = s1.stu_id 
AND s.id = s2.stu_id 
AND s1.c_name = '计算机'
AND s2.c_name = '英语';

#将计算机考试成绩按从高到低进行排序
SELECT score.* FROM score 
WHERE c_name = '计算机' 
ORDER BY grade ASC;

#从student表和score表中查询出学生的学号，然后合并查询结果
SELECT student.id 
FROM student, score 
WHERE student.id = score.stu_id;

#查询姓张或者姓王的同学的姓名、院系和考试科目及成绩
SELECT student.name, student.department, score.c_name, score.grade 
FROM score, student 
WHERE (student.name LIKE '王%' OR student.name LIKE '李%' )
AND student.id = score.stu_id ;

#查询都是湖南的学生的姓名、年龄、院系和考试科目及成绩
SELECT student.name, student.birth, student.department, score.c_name, score.grade 
FROM student, score 
WHERE address LIKE '湖南%' 
AND student.id = score.stu_id ;