数据库多表查询（linux下）----创建数据库名mydb11_stu

一、创建数据库mydb11_stu,创建表student、score

1.创建数据库mydb11_stu

create database mydb11_stu;
use mydb11_stu

2.创建带有条件的表student和score

create table student(id int(10) not NULL unique primary key, name varchar(20) not NULL,sex varchar(4), birth_year varchar(20), 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));

二、向表中插入数据

1.表student

insert student values(901,'张三丰','男',2002,'计算机系','北京市海淀区');
insert student values(902,'周全有','男',2000,'中文系','北京市昌平区');
insert student values(903,'张思维','女',2003,'中文系','湖南省永州市');
insert student values(904,'李广昌','男',1999,'英语系','辽宁市阜新区');
insert student values(905,'王翰','男',2004,'英语系','福建省厦门市');
insert student values(906,'王心凌','女',1998,'计算机系','湖南省衡阳市');

2.表score

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',49);
insert into score values(null,906,'英语',83);

三、条件查询

1.分别查询student表和score表的所有记录

SELECT * FROM student;
SELECT * FROM score;

2.查询student表的第2条到5条记录

select * from student limit 1, 4;

3.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');

4.从student表中查询年龄小于22岁的学生信息

select * from student where birth_year > 2003;

5.从student表中查询每个院系有多少人

select department, count(*) as num_student from student group by department;

6.从score表中查询每个科目的最高分

select c_name , max(grade) as max_grade from score group by c_name;

7.查询李广昌的考试科目（c_name）和考试成绩（grade）

 select c_name, grade from  score where stu_id = (select id from student where name = '李广昌');

8.用连接的方式查询所有学生的信息和考试信息

 select student.*, score.c_name, score.grade from student left join score on student.id = score.stu_id;

9.计算每个学生的总成绩

select stu_id, sum(grade) as total_grade from score group by stu_id;

10.计算每个考试科目的平均成绩

select c_name , avg(grade) as avg_grade from score group by c_name;

11.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 c_name = '计算机' and grade < 95 ;

12.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;

13.从student表和score表中查询出学生的学号，然后合并查询结果

select student.id from student union select stu_id from score;

14.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 name, department, c_name, grade from student join score on student.id = score.stu_id where name like '张%' or name like '王%';

15.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,student.birth_year,student.department,score.c_name,score.grade from student join score on student.id =score.stu_id where student.address like '%湖南%';