一、准备数据
1、创建数据库
mysql> create database if not exists school character set utf8;
Query OK, 1 row affected, 1 warning (0.00 sec)
2、进入数据库创建表
#进入数据库
mysql> use school
Database changed
mysql> select database();
+------------+
| database() |
+------------+
| school |
+------------+
1 row in set (0.00 sec)
#创建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)
);
#创建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)
);
3、表中插入数据记录
#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);4、查看表结构及表内数据
mysql> desc student;
+------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------+-------------+------+-----+---------+-------+
| id | int(10) | NO | PRI | NULL | |
| name | varchar(20) | NO | | NULL | |
| sex | varchar(4) | YES | | NULL | |
| birth | year(4) | YES | | NULL | |
| department | varchar(20) | YES | | NULL | |
| address | varchar(50) | YES | | NULL | |
+------------+-------------+------+-----+---------+-------+
6 rows in set (0.00 sec)
mysql> desc score;
+--------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| id | int(10) | NO | PRI | NULL | auto_increment |
| stu_id | int(10) | NO | | NULL | |
| c_name | varchar(20) | YES | | NULL | |
| grade | int(10) | YES | | NULL | |
+--------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
mysql> select * from student;
+-----+-----------+------+-------+--------------+--------------------+
| id | name | sex | birth | department | address |
+-----+-----------+------+-------+--------------+--------------------+
| 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 |
+-----+-----------+------+-------+--------------+--------------------+
6 rows in set (0.00 sec)
mysql> select * from score;
+----+--------+-----------+-------+
| id | stu_id | c_name | grade |
+----+--------+-----------+-------+
| 1 | 901 | 计算机 | 98 |
| 2 | 901 | 英语 | 80 |
| 3 | 902 | 计算机 | 65 |
| 4 | 902 | 中文 | 88 |
| 5 | 903 | 中文 | 95 |
| 6 | 904 | 计算机 | 70 |
| 7 | 904 | 英语 | 92 |
| 8 | 905 | 英语 | 94 |
| 9 | 906 | 计算机 | 90 |
| 10 | 906 | 英语 | 85 |
+----+--------+-----------+-------+
10 rows in set (0.00 sec)
二、查询
1.查询student表的所有记录
mysql> select * from student; 
2.查询student表的第2条到4条记录
mysql> 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
mysql> 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
mysql> 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
mysql> select * from student
-> where year(now())-birth between 18 and 22; 
6.从student表中查询每个院系有多少人
mysql> select department,count(department) number
-> from student
-> group by department; 
7.从score表中查询每个科目的最高分
mysql> select c_name 科目,max(grade) 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）
mysql> select a.id,a.name,b.c_name,b.grade from student a inner join score b
-> on a.id=b.stu_id
-> and a.name='李四'; 
9.用连接的方式查询所有学生的信息和考试信息
mysql> select * from score a left join student b
-> on a.stu_id=b.id; 
10.计算每个学生的总成绩
mysql> select a.id,a.name,sum(b.grade) from student a left join score b
-> on a.id=b.stu_id
-> group by b.stu_id; 
11.计算每个考试科目的平均成绩
mysql> 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
mysql> 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
#方法1：
mysql> 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');
#方法2：
mysql> select * from student where id in (
-> select b.stu_id from (select * from score where c_name='计算机') b inner join
-> (select * from score where c_name='英语') c
-> on b.stu_id=c.stu_id
-> where b.stu_id=c.stu_id); 
14.将计算机考试成绩按从高到低进行排序
mysql> select stu_id,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
mysql> 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 a.name,a.department,b.c_name,b.grade from student a inner join score b
-> on a.id=b.stu_id
-> where a.name like '张%' or a.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
mysql> select a.name,2021-a.birth age,a.department,b.c_name,b.grade
-> from student a inner join score b
-> on a.id=b.stu_id
-> where a.address like '%湖南%'; 