MySQL 表的连接

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

2.1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');

2.2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.表的查询

1.查询student表的所有记录

Select * from student;

2.查询student表的第2条到4条记录

select * from student limit 2,4;

3.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;

4.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';

5.从student表中查询年龄18~22岁的学生信息

select * from student where (2023 - birth ) between 18 and 60 ;

6.从student表中查询每个院系有多少人

select count(*),department  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（grade）

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

10.计算每个学生的总成绩

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

11.计算每个考试科目的平均成绩

select c_name,avg(grade) from score inner join student on student.id=score.stu_id group by c_name;

12.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_id  where c_name='计算机' and grade < 95;

13.查询同时参加计算机和英语考试的学生的信息

select * from student where id in (select a.stu_id from score a left join score b on a.stu_id=b.stu_id where a.c_name='计算机' and b.c_name='英语');

14.将计算机考试成绩按从高到低进行排序

select c_name,grade from score  where c_name='计算机' order by grade desc;

15.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;

16.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 inner join score on student.id=score.stu_id where student.name regexp '^[张王]';

或者select name,department,c_name,grade from student inner join score on student.id=score.stu_id where student.name  like

'张%' or student.name like '王%';

17.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,(2023-birth),department,c_name,grade from student inner join score on student.id=score.stu_id where student.address like '湖南省%';

或者select name,(2023-birth),department,c_name,grade from student inner join score on student.id=score.stu_id where student.address regexp '^[湖南省]';