MySQL多表查询

作业要求：

 作业第一条第二条代码已给

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

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 limit 1, 3;

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 in ('计算机系', '英语系');

7.从student表中查询年龄18~22岁的学生信息（根据已有年份随便写了年份区间）

select * from student where birth between 1987 and 1992;

8.从student表中查询每个院系有多少人

select department, count(*) as number 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 c_name, grade from score inner join student on score.stu_id = student.id where student.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 score inner join student on score.stu_id=student.id;

12.计算每个学生的总成绩

select stu.name, sum(sc.grade) from score as sc right join student as stu on stu.id=sc.stu_id group by stu.id;

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 stu.*, sc.* from score as sc inner join student as stu on stu.id = sc.stu_id 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 a.* from score as sc inner join (select stu.* from student as stu inner join score as sc on sc.stu_id=stu.id where sc.c_name='计算机') as a on a.id = sc.stu_id where sc.c_name='英语';

16.将计算机考试成绩按从高到低进行排序

select stu.*, sc.* from score sc inner JOIN student stu on sc.stu_id = stu.id where sc.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 stu.name, stu.department, sc.c_name, sc.grade from student as stu inner join score as sc on sc.stu_id = stu.id where stu.name like '张%' or stu.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 name, (year(now())-birth) as age, department,c_name, grade from score, (select * from student where address like '湖南%') as stu where stu.id = stu_id;