数据库练习3
首先插入数据：
create database mydb11_stu;
use mydb11_stu;
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_idint int(10) not null,c_name varchar(20),grade int(10));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','辽宁省皋新市');
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');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);
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, count(*) from student group by department;
6.从score表中查询每个科目的最高分
select score.c_name,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 score.c_name,score.grade from score join student on score.stu_idint=student.id 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 * from score join student on score.stu_idint=student.id;
9.计算每个学生的总成绩
select name,sum(grade) from student inner join score on student.id= score.stu_idint group by name;
10.计算每个考试科目的平均成绩
select c_name,avg(grade) from student inner join score on student.id= score.stu_idint group by c_name;
11.查询计算机成绩低于95的学生信息
select * from student left join score on student.id= score.stu_idint 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 name, score.c_name,grade from student left join score on student.id= score.stu_idint 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 id from student union select stu_idint 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 student.name,department,score.c_name,grade from student left join score on student.id=score.stu_idint where student.name like '张%' or student.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,(year(now())-birth),department,score.c_name,grade from student left join score on student.id=score.stu_idint where student.address like "湖南%";
