多表查询

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);

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 WHERE id>=902 AND id <=904;

5.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;

6.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';

7.从student表中查询年龄18~22岁的学生信息

SELECT * FROM student WHERE birth>=1998 AND birth <=2002;

8.从student表中查询每个院系有多少人

SELECT department,count(*) FROM student GROUP BY department;

9.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;

10.查询李四的考试科目（c_name）和考试成绩（grade）

SELECT s.name as name,sc.c_name as c_name,sc.grade as grade FROM student as s join score as sc ON(s.id = sc.stu_id) WHERE 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 * from student as s JOIN score as sc on(s.id=sc.stu_id);

12.计算每个学生的总成绩

SELECT student.id as id,name,SUM(grade) FROM student,score WHERE student.id=score.stu_id GROUP BY id;

13.计算每个考试科目的平均成绩

SELECT c_name,AVG(grade) FROM score GROUP BY c_name;

14.查询计算机成绩低于95的学生信息

SELECT * FROM student WHERE id IN(SELECT stu_id FROM score WHERE c_name="计算机" and grade<95);

15.查询同时参加计算机和英语考试的学生的信息

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

16.将计算机考试成绩按从高到低进行排序

SELECT stu_id, grade FROM score WHERE c_name= '计算机' ORDER BY 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 student.id, name,sex,birth,department, address, c_name,grade FROM student, score WHERE(name LIKE '张%' OR name LIKE '王%')AND student.id=score.stu_id ;

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 student.id, name,sex,birth,department, address, c_name,grade FROM student, score WHERE address LIKE '湖南%' AND student.id=score.stu_id;

本文地址：https://blog.csdn.net/qq_44923097/article/details/108987059