MySQL每日一练：单表查询、连接查询

news2024/11/23 19:03:02

1、创建两张表

student表：

score表：

2.为student表和score表增加记录

student表：

score表：

3、按条件查找

1、创建两张表

student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)
);

score表：

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

student表：

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');

score表：

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、按条件查找

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 2,3;

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='计算机系' or department='英语系';

select * from student where department in('计算机系','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)<=22 and (2023-birth)>=18;

6.从student表中查询每个院系有多少人

select department,count(*) as 部门人数 from student group by department;
t;

7.从score表中查询每个科目的最高分

select c_name,max(grade) as 最高分 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 student.name,c_name,grade 
from score 
join student 
on student.id=score.stu_id 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.*,score.c_name,score.grade 
from score 
join student 
on student.id=score.stu_id ;

10.计算每个学生的总成绩

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

11.计算每个考试科目的平均成绩

select c_name,avg(grade) as 平均分 from score group by c_name;

12.查询计算机成绩低于95的学生信息

select student.*,grade 
from score 
join student 
on student.id=score.stu_id wheregrade<90 and c_name='计算机';

13.查询同时参加计算机和英语考试的学生的信息

SELECT s.id, s.name, s.sex, s.birth, s.department, s.address 
FROM student s 
INNER JOIN score sc 
ON s.id = sc.stu_id 
WHERE sc.c_name = '计算机' AND sc.stu_id IN ( SELECT stu_id FROM score WHERE c_name = '英语' );

14.将计算机考试成绩按从高到低进行排序

select * 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 student.*,score.* from score join student on student.id=score.stu_id;

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 student.name,student.department,score.c_name,score.grade 
from score 
join student 
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 student.name,student.department,score.c_name,score.grade,student.address from score 
join student 
on student.id=score.stu_id 
where address like '湖南省%';