MySQL必学！！！！练习题（多表查询）

一、搭建环境

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)
);
创建score表。SQL代码如下：
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
向student表插入记录的INSERT语句如下：
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');
向score表插入记录的INSERT语句如下：
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);

二、多表查询

1.查询student表的所有记录

SELECT * FROM student;

2查询student表的第2条到4条记录

SELECT * FROM student LIMIT 3 OFFSET 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;

4.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 = '计算机系' OR department = '英语系';

5.从student表中查询年龄18~22岁的学生信息

SELECT * FROM student WHERE year(now())-birth BETWEEN 18 AND 22;

6.从student表中查询每个院系有多少人

SELECT department, COUNT(*) as num_students 
FROM student GROUP BY department;

7.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;

8.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 = (SELECT id FROM student WHERE name = '李四');

9.用连接的方式查询所有学生的信息和考试信息

SELECT s.*, sc.* FROM student s JOIN score sc ON s.id = sc.stu_id;

10.计算每个学生的总成绩

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

11.计算每个考试科目的平均成绩

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

12查询计算机成绩低于95的学生信息

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

13.查询同时参加计算机和英语考试的学生的信息

SELECT s.name   FROM student s 
  JOIN score sc1 ON s.id = sc1.stu_id   
  JOIN score sc2 ON s.id = sc2.stu_id 
  WHERE sc1.c_name = '计算机' AND sc2.c_name = '英语';

14.将计算机考试成绩按从高到低进行排序

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

15.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 AS 学号 FROM student   
UNION ALL   
SELECT stu_id FROM score;

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

17.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 s.name, s.birth, s.department, sc.c_name, sc.grade   
FROM student s   
JOIN score sc ON s.id = sc.stu_id   
WHERE s.address LIKE '%湖南省%';