mysql小代码练习

CREATE TABLE student(
    id INT(10) NOT NULL UNIQUE PRIMARY KEY,
    name VARCHAR(20) NOT NULL,
    sex VARCHAR(4),
    birth INT,
    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)
);



INSERT INTO student VALUES
    (901,'张老大', '男',1985,'计算机系', '北京市海淀区'),
    (902,'张老二', '男',1986,'中文系', '北京市昌平区'),
    (903,'张三', '女',1990,'中文系', '湖南省永州市'),
    (904,'李四', '男',1990,'英语系', '辽宁省阜新市'),
    (905,'王五', '女',1991,'英语系', '福建省厦门市'),
    (906,'王六', '男',1988,'计算机系', '湖南省衡阳市');

INSERT INTO score VALUES
    (NULL,901, '计算机',98),
    (NULL,901, '英语',80),
    (NULL,902, '计算机',65),
    (NULL,902, '中文',88),
    (NULL,903, '中文',96),
    (NULL,904, '计算机',70),
    (NULL,904, '英语',92),
    (NULL,905, '英语',94),
    (NULL,906, '计算机',90),
    (NULL,906, '英语',85);



--1.查询student表的所有信息
select * from student;


--2.查询student表的第2条到第4条记录
select * from student limit 1,3;


--3.从student表查询所有学生的学号(id),姓名(name),院系(department)的信息
select id,name,department from student;


--4.从student表中查询计算机和英语系的学生的信息
select * from student where department in ('计算机系','英语系');
select * from student where department='计算机系' or department='英语系');


--5.从student表中查询1988-1990的学生信息
select * from student where birth between 1988 and 1990;
select * from student where birth >=1988 and birth<=1990;


--6.从student表中查询每个院系有多少人
select department,count(*) from student group by department;


--7.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;


--8.查询李四的考试科目(c_name)和考试成绩
select name,c_name,grade
from student
join score on student.id = score.stu_id
where name='李四'; 


select c_name,grade
from score
where stu_id=(select id from student where name='李四');


--9.用连接的方式查询所有学生的信息和考试信息
select *
from student
join score on student.id = score.stu_id;


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


--10.计算每个学生的总成绩
select student.id,name,sum(grade)
from student
join score on student.id = score.stu_id
group by student.id;


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


--11.计算每个考试科目的平均成绩
select c_name,avg(grade)
from score
group by c_name;


--12.查询计算机成绩低于95的学生信息
select name,sex ,birth,department,address,c_name,grade
from student
join score on student.id = score.stu_id
where c_name='计算机' and grade<95;


--13.将计算机考试成绩按从高到低进行排序
select grade
from score
where c_name='计算机'
order by grade desc;


--14.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;


--15.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,score
where student.id=score.stu_id and (name like '张%' or name like '王%');


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


--16.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,department,c_name,grade
from student,score
where student.id=score.stu_id and address like '湖南%';