第三次作业

1.创建数据库

create database myde11_stu;

2.使用库

use myde11_stu;

3.创建studnet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));

4.创建score表

 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));

5.给student，score表插入数据

（1）向student表插入记录如下：
mysql> insert  student values(901,'张三丰','男',2002,'计算机系','北京市海淀区');
mysql> insert  student values(902,'周全有','男',2000,'中文系','北京市昌平区');
mysql> insert  student values(903,'张思维','女',2003,'中文系','湖南省永州市');
mysql> insert  student values(904,'李广昌','男',1999,'英语系','辽宁省皋新市');
mysql> insert  student values(905,'王翰','男',2004,'英语系','福建省厦门市');
mysql> insert  student values(906,'王心凌','女',1998,'计算机系','湖南省衡阳市');

    （2）向score表插入记录如下：
mysql> insert into score values(null,901,'计算机',98);
mysql> insert into score values(null,901,'英语',80);
mysql> insert into score values(null,902,'计算机',65);
mysql> insert into score values(null,902,'中文',88);
mysql> insert into score values(null,903,'中文',95);
mysql> insert into score values(null,904,'计算机',70);
mysql> insert into score values(null,904,'英语',92);
mysql> insert into score values(null,905,'英语',94);
mysql> insert into score values(null,906,'计算机',49);
mysql> insert into score values(null,906,'英语',83);

（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='计算机系' or department='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 year(now())-birth<22;

(5)从student表中查询每个院系有多少人

select department 各院系,count(*) 各院系人数 from student wheretrue group by department;

(6)从score表中查询每个科目的最高分

select c_name,max(grade) from score where 1=1 group by c_name;

(7)查询李广昌的考试科目(c_name)和考试成绩(grade)

select st.name,sc.c_name,sc.grade from score sc join student st on st.id=sc.stu_id where st.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 * from student st inner join score sc on  st.id=sc.stu_id;

select * from student,score where student.id=score.stu_id;

(9)计算每个学生的总成绩

select st.name 学生,sum(sc.grade) 总成绩 from student st join score sc on st.id=sc.stu_id where 1=1 group by st.name;

(10)计算每个考试科目的平均成绩

select c_name,round(avg(grade),2) from score wheretrue  group by c_name;

(11)查询计算机成绩低于95的学生信息

select * from student st join score sc on st.id=sc.stu_id where sc.c_name='计算机' and sc.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 * from student st,score sc where st.id=sc.stu_id;

(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 st.name,st.department,sc.c_name,sc.grade from student st join score sc on st.id=sc.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 st.name,st.birth,st.department,sc.c_name,sc.grade from student st join score sc on st.id=sc.stu_id where address like '湖南%';