1. 创建表

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),
    FOREIGN KEY (stu_id) REFERENCES student(id)
);

2.向 student 表和 score 表插入记录

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);

3. 查询

查询 student 表的所有记录

SELECT * FROM student;

查询 student 表的第2条到第4条记录

SELECT * FROM student LIMIT 1, 3;

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18~22岁的学生信息

SELECT * FROM student WHERE YEAR(CURDATE()) - birth BETWEEN 18 AND 22;

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 c_name, grade FROM score WHERE stu_id = 904;

用连接的方式查询所有学生的信息和考试信息

SELECT student.id, student.name, student.sex, student.birth, student.department, student.address,
       score.c_name, score.grade
FROM student
JOIN score ON student.id = score.stu_id;

计算每个学生的总成绩

SELECT stu_id, SUM(grade) AS total_grade
FROM score
GROUP BY stu_id;

 

计算每个考试科目的平均成绩

SELECT c_name, AVG(grade) AS average_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 student 
JOIN score ON student.id = score.stu_id
WHERE score.c_name = '计算机' AND score.grade < 95;

 

查询同时参加计算机和英语考试的学生的信息

SELECT student.* 
FROM student
JOIN score AS score1 ON student.id = score1.stu_id AND score1.c_name = '计算机'
JOIN score AS score2 ON student.id = score2.stu_id AND score2.c_name = '英语';

将计算机考试成绩按从高到低进行排序

SELECT * FROM score WHERE c_name = '计算机' ORDER BY grade DESC;

 

从student表和score表中查询出学生的学号，然后合并查询结果

SELECT id FROM student
UNION
SELECT stu_id FROM score;

 

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 student
JOIN score ON student.id = score.stu_id
WHERE student.name LIKE '张%' OR student.name LIKE '王%';

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, YEAR(CURDATE()) - student.birth AS age, student.department, score.c_name, score.grade
FROM student
JOIN score ON student.id = score.stu_id
WHERE student.address LIKE '湖南%';