MYSQL学习笔记

sql(structured query lanaguage) 结构化查询语言

创建一个名称为mydb1的数据库
create database mydb1;

显示所有数据库
show databases;

创建一个使用utf-8字符集的mydb2数据库。
create database mydb2 character set utf8;

创建一个使用utf-8字符集，并带校对规则的mydb3数据库
create database mydb3 character set utf8 collate utf8_general_ci;

查看前面创建的mydb2数据库的定义信息
show create database mydb2;

删除前面创建的mydb1数据库
drop database mydb1;

查看服务器中的数据库，并把mydb2库的字符集修改为gb2312;
alter database mydb2 character set gb2312;

备份mydb3库中的数据，并恢复
1.准备数据并备份
use mydb3;
create table test (id int);
insert into test(id) values(1);

备份（退到window命令行窗口）：mysqldump -u root -p mydb3>c:\test.sql

2.恢复：
mysql -uroot -p
create database mydb3;
use mydb3;
source c:\test.sql
创建一个员工表
create table employee
(
id int,
name varchar(20),
sex varchar(4),
birthday date,
entry_date date,
job varchar(100),
salary double,
resume text
)character set utf8 collate utf8_general_ci;

在上面员工表的基本上增加一个image列。
alter table employee add image blob;

查看表
desc employee;

修改job列，使其长度为60。
alter table employee modify job varchar(60);

删除sex列
alter table employee drop sex;

表名改为user
rename table employee to user;

修改表的字符集为utf-8
alter table user character set utf8;

查看表的字符集
show create table user;(表的创建语句)

列名name修改为username
alter table user change column name username varchar(20);

使用insert语句向表中插入三个员工的信息。
rename table user to employee;
insert into employee(id,username,birthday,entry_date,job,salary,resume) values(1,’aaa’,’1980-09-09’,’1980-09-09’,’bbb’,90,’aaaa’);
insert into employee(id,username,birthday,entry_date,job,salary,resume) values(2,’bbb’,’1980-09-09’,’1980-09-09’,’bbb’,90,’aaaa’);
查看插入的数据
select * from employee;

插入中文数据
insert into employee(id,username) values(2,’小李子’);
show variables like ‘chara%’;
set character_set_cilent=gb2312;
insert into employee(id,username) values(2,’小李子’);
查询时如果发生乱码：
set character_set_results=gb2312;
select * from employee;

将所有员工薪水修改为5000元。
update employee set salary=5000;

将姓名为’aaa’的员工薪水修改为3000元。
update employee set salary=3000 where username=’aaa’;

将姓名为’aaa’的员工薪水修改为4000元,job改为ccc。
update employee set salary=4000,job=’ccc’ where username=’aaa’;

将aaa的薪水在原有基础上增加1000元。
update employee set salary=salary+1000 where username=’aaa’;

删除表中名称为’zs’的记录
delete from employee where username=’aaa’;

删除表中所有记录。
delete from employee;

使用truncate删除表中记录
truncate table employee

执行sql脚本
source c:\student.sql

查询表中所有学生的信息。
select * from student;

查询表中所有学生的姓名和对应的英语成绩。
select name,english from student;

过滤表中重复数据。
select distinct english from student;

在所有学生总分上加10分特长分。
select name,(english+chinese+math)+10 from student;

使用别名表示学生分数。
select name as 姓名,(english+chinese+math)+10 as 总分 from student;
select name 姓名,(english+chinese+math)+10 总分 from student;

查询姓名为wu的学生成绩
select * from student where name=’王五’

查询英语成绩大于90分的同学
select name from student where english>90;

查询总分大于200分的所有同学
select name from student where (english+chinese+math)>200;

查询英语分数在 80－90之间的同学
select name from student where english>80 and english<90;
select name from student where english between 80 and 90;

查询数学分数为89,90,91的同学
select * from student where math=80 or math=90 or math=91;
select * from student where math in(80,90,91);

查询所有姓李的学生成绩。
select * from student where name like ‘李%’

查询数学分>80，语文分>80的同学。
select name from student where math>80 and chinese>80;

对数学成绩排序后输出
select * from student order by math;

对总分排序后输出，然后再按从高到低的顺序输出
select * from student order by (math+english+chinese) desc;

对姓李的学生成绩排序输出
select * from student where name like ‘李%’ order by (math+english+chinese);

统计一个班级共有多少学生？
select count(*) from student;

统计数学成绩大于90的学生有多少个？
select count(*) from student where math>90;

统计总分大于250的人数有多少？
select count(*) from student where (math+english+chinese)>250;

统计一个班级数学总成绩？
select sum(math) from student;

统计一个班级语文、英语、数学各科的总成绩
select sum(chinese),sum(english),sum(math) from student;

统计一个班级语文、英语、数学的成绩总和
select sum(chinese+math+english) from student;

统计一个班级语文成绩平均分
select sum(chinese)/count(chinese) from student;

求一个班级数学平均分？
select avg(math) from student;

求一个班级总分平均分
select avg(math+english+chinese) from student;

求班级最高分和最低分
select max(math+english+chinese),min(math+english+chinese) from student;

第6种形式的select:
create table orders(
id int,
product varchar(20),
price float
);

insert into orders(id,product,price) values(1,’电视’,900);
insert into orders(id,product,price) values(2,’洗衣机’,100);
insert into orders(id,product,price) values(3,’洗衣粉’,90);
insert into orders(id,product,price) values(4,’桔子’,9);
insert into orders(id,product,price) values(5,’洗衣粉’,90);

对订单表中商品归类后，显示每一类商品的总价
select product,sum(price) from orders group by product;

查询购买了几类商品，并且每类总价大于100的商品
select product from orders group by product where sum(price)>100;×
select product from orders group by product having sum(price)>100;

主键约束
create table test1
(
id int primary key,
name varchar(20)
);

主键自动增长：
create table test2
(
id int primary key auto_increment,
name varchar(20)
);

唯一约束和非空约束
create table user
(
id int primary key auto_increment,
username varchar(40) not null unique,
password varchar(40) not null,
email varchar(100) not null unique
);

外键约束
create table male
(
id int primary key auto_increment,
name varchar(40)
);

create table female
(
id int primary key auto_increment,
name varchar(40),
male_id int,
constraint male_id_FK foreign key(male_id) references male(id)
);

创建部门表和员工表(一对多或多对一)
create table department
(
id int primary key auto_increment,
name varchar(100)
);

create table employee
(
id int primary key auto_increment,
name varchar(100),
salary double,
department_id int,
constraint department_id_FK foreign key(department_id) references department(id)
);

创建学生、老师表（多对多）
create table teacher
(
id int primary key auto_increment,
name varchar(100),
salary double
);

create table student
(
id int primary key auto_increment,
name varchar(100)
);

create table teacher_student
(
teacher_id int,
student_id int,
primary key(teacher_id,student_id),
constraint teacher_id_FK foreign key(teacher_id) references teacher(id),
constraint student_id_FK foreign key(student_id) references student(id)
);

insert into teacher(name,salary) values(‘老王’,1000);
insert into teacher(name,salary) values(‘老李’,1000);

insert into student(name) values(‘aaa’);
insert into student(name) values(‘bbb’);
insert into student(name) values(‘ccc’);

insert into teacher_student(teacher_id,student_id) values(1,1);
insert into teacher_student(teacher_id,student_id) values(1,2);
insert into teacher_student(teacher_id,student_id) values(1,3);
insert into teacher_student(teacher_id,student_id) values(2,1);

已知老师的id为1，查询出1号老师所有的学生
select s.* from teacher_student t_s,student s where teacher_id=1 and t_s.student_id=s.id;

1号学生有几个老师
select teacher.* from teacher_student,teacher where student_id=1 and teacher_student.teacher_id=teacher.id;

创建人、身份证表（一对一）
create table person
(
id int primary key auto_increment,
name varchar(30)
);

create table idcard
(
id int primary key,
num varchar(30) not null unique,
constraint person_id_FK foreign key(id) references person(id)
);