MySQL学习（4）多表查询

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)

);

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(10)

);

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);

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

查询连续的多行记录(第n~m行)select * from table1  limit n-1,m-n+1;

select * from student limit 1,3;

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 = '英语系' or department = ' 计算机系';

5.从student表中查询年龄18~22岁的学生信息

select * from student where birth < 2003 and birth > 1999 ;

简单做个减法当前时间 - 18 or 22 要注意大小。

6.从student表中查询每个院系有多少人

select department,count(1) 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 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 student.id,name,sex,birth,department,address,c_name,grade 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,score where student.idd= score.stu_id group by 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 * from student where id in (select stu_id from score 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 = any(select stu_id from score where stu_id in ( select stu_id from score where c_name = '计算机') and c_name = '英语');

14.将计算机考试成绩按从高到低进行排序

SELECT stu_id, 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

mysql> SELECT student.id, name,sex,birth,department, address, c_name,grade
    -> FROM student, score
    -> WHERE
    -> (name LIKE '张%' OR name LIKE '王%')
    -> and student.id=score.stu_id ;