mysql多表查询

1.创建student和score表

CREATE TABLE student (
    id INT(10) NOT NULL PRIMARY KEY UNIQUE,
    name VARCHAR(20) NOT NULL,
    sex VARCHAR(4),
    birth YEAR,
    department VARCHAR(20),
    address VARCHAR(50)
);

创建score表。SQL代码如下：
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(1sh0)
);

2.为student表和score表增加记录
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');

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.查询student表的所有记录

4.查询student表的第2条到4条记录

select * from student limit 1,4;

5.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;

6.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';

7.从student表中查询年龄18~22岁的学生信息

select * from student where birth>=1986 and birth<=1990;

8.从student表中查询每个院系有多少人

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

9.从score表中查询每个科目的最高分

select c_name as 科目,max(grade) as 最高分 from score group by c_name;

10.查询李四的考试科目（c_name）和考试成绩（grade）

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

11.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 where student.id=score.stu_id;

12.计算每个学生的总成绩

select name,sum(grade) as 总成绩 from student join score where student.id=score.stu_id group by name;

13.计算每个考试科目的平均成绩

select c_name as 科目,avg(grade) as 平均成绩 from student join score where student.id=score.stu_id group by c_name;

14.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;

15.查询同时参加计算机和英语考试的学生的信息

select * from student left join (select stu_id ,count(*) as 科目数 from score where c_name='计算机' or c_name='英语' group by stu_id) as c2 on c2.stu_id=student.id where 科目数>1;

16.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;

17.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;

18.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 (select id,name,department from student where name regexp '^张' or name regexp '^王') as s1 join score where s1.id=score.stu_id;

19.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 (select id,name,department from student where address regexp '^湖南省' or address regexp '^湖南省') as s1 join score where s1.id=score.stu_id;