多表查询练习

1. 创建 student 和 score 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)
);

2. 为 student 表和 score 表增加记录

INSERT INTO student VALUES
(901,'张老大', '男',1985,'计算机系', '北京市海淀区'),
(902,'张老二', '男',1986,'中文系', '北京市昌平区'),
(903,'张三', '女',1990,'中文系', '湖南省永州市'),
(904,'李四', '男',1990,'英语系', '辽宁省阜新市'),
(905,'王五', '女',1991,'英语系', '福建省厦门市'),
(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),
(NULL,901, '英语', 80),
(NULL,902, '计算机',65),
(NULL,902, '中文',88),
(NULL,903, '中文',95),
(NULL,904, '计算机',70),
(NULL,904, '英语',92),
(NULL,905, '英语',94),
(NULL,906, '计算机',90),
(NULL,906, '英语',85);

3. 查询 student 表的所有记录

SELECT * FROM student;

4. 查询 student 表的第 2 条到 4 条记录

SELECT * FROM student LIMIT 1, 3;

5. 查询所有学生的学号、姓名和院系的信息

SELECT id, name, department FROM student;

6. 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');

7. 查询年龄 18~35岁的学生信息

SELECT *, YEAR(CURDATE()) - birth AS age FROM student WHERE YEAR(CURDATE()) - birth BETWEEN 18 AND 35;

8. 查询每个院系有多少人

SELECT department, COUNT(*) AS 人数 FROM student GROUP BY department;

9. 查询每个科目的最高分

SELECT c_name, MAX(grade) AS 最高分 FROM score GROUP BY c_name;

10. 查询李四的考试科目和考试成绩

SELECT s.c_name, s.grade FROM score s JOIN student st ON s.stu_id = st.id WHERE st.name = '李四';

11. 用连接的方式查询所有学生的信息和考试信息

SELECT st.*, s.c_name, s.grade FROM student st LEFT JOIN score s ON st.id = s.stu_id;

12. 计算每个学生的总成绩

SELECT st.id, st.name, SUM(s.grade) AS 总成绩 FROM student st LEFT JOIN score s ON st.id = s.stu_id GROUP BY st.id, st.name;

13. 计算每个考试科目的平均成绩

SELECT c_name, AVG(grade) AS 平均成绩 FROM score GROUP BY c_name;

14. 查询计算机成绩低于 95 的学生信息

SELECT st.* FROM student st JOIN score s ON st.id = s.stu_id WHERE s.c_name = '计算机' AND s.grade < 95;

15. 查询同时参加计算机和英语考试的学生的信息

SELECT st.* FROM student st WHERE st.id IN (SELECT stu_id FROM score WHERE c_name = '计算机') AND st.id IN (SELECT stu_id FROM score WHERE c_name = '英语');

16. 将计算机考试成绩按从高到低进行排序

SELECT st.name, s.grade FROM student st JOIN score s ON st.id = s.stu_id WHERE s.c_name = '计算机' ORDER BY s.grade DESC;

17. 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;

18. 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 st.name, st.department, s.c_name, s.grade FROM student st JOIN score s ON st.id = s.stu_id WHERE st.name LIKE '张%' OR st.name LIKE '王%';

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