DDL(Data Definition Language)：数据库定义语句；
DML(Data Manipulation Language)：用于增删改查数据库中数据；
DCL(Data Control Language)用来向用户赋予/取消对数据对象的控制权限；
TCL(Transaction Control Language)：用来对事务进行管理
数据库登录：
win+R运行cmd,输入 双引号里面的内容："mysql -uroot -proot"回车，root为用户名和密码。
注意：执行win命令，最后不需要加“;”，但执行mysql语句则需要加“;”
一、库操作1.创建名为"mydb1"数据库:
create database mydb1;2.显示所有数据库:
show databases;3.创建名为"mydb1"并带字符集的数据库:
create database mydb2 CHARACTER SET=utf8;4.显示数据库mydb2创建语句:
show create database mydb2;5.如果存在数据库mydb2，则删除mydb2（如果不加上if exits判断,一旦要删除的数据库不存在，就会报错）:
drop database if exits mydb2;6.修改数据库的库字符编码:
alter database mydb2 character set gb2312;7.数据库备份(root是用户名，这是一个win命令(即打开cmd，直接输入)，将数据库备份到c盘下):
mysqldump -u root -p mydb2>c://test.sql;8.数据库恢复（两种方式）:
(1)这是一个win命令:mysql -u root -p mydb2
(2)source c://test.sql;
二、表操作1.创建学生表:
create table student(/* 直接指定主键，也可单独指定*/
sno varchar(4) primary key,
sname varchar(10) not null,
sage int,
ssex char(2),
email varchar(20) unique,
constraint ck_student_ssex_sage check(ssex in('男','女')and sage between 10 and 50)
)
2.增加列(字段):
alter table tableName add columnName varchar(30);3.修改列，改变长度:
alter table tableName modify cloumnName varchar(60);4.删除列:
alter table tableName drop column cloumnName;5.修改表名:
rename table tableName_old to tableName_new;6.修改表的字符集:
alter table user character set gbk;7.修改列名:
alter table tableName change column cloumnName columnName_new varchar(60);8.删除表:
drop table tableName;三、增删改查
准备表
create table employee(
id int,
name varchar(40),
sex varchar(4),
birthday date,
entry_date date,
salary decimal(8,2),
resume text
);
1.插入数据:
insert into employee(id,name,sex,birthday,entry_date,salary,resume) values(1,'zhangsan','male','1993-03-04','2016-11-10','1000','i am a developer');/*可以省略表字段，但是必须插入全部字段*/
insert into employee values(1,'zhangsan','male','1993-03-04','2016-11-10','1000','i am a developer');
2.指定某些列插入数据:
insert into employee(id) values(6);3.查看汉字时不乱码:
insert into employee(id,name) values(6,'张三');/*告诉mysql客户采用gb2312编码*/
show variables like 'chara%';
set character_set_client=gb2312;
insert into employee(id,username) values('3','张三');
/*查看汉字时不乱码*/
show variables like 'chara%';
set character_set_results=gb2312;
select * from employee;
4.删除表数据:
/*删除表中名称为’zs’的记录*/delete from employee where name='zs';
/*删除表中所有记录*/
delete from employee;
/*使用truncate删除表中记录(快速删除表中所有数据，保留表的数据结构)*/
truncate table employee;
5.修改表中数据:
/*将所有员工薪水修改为5000元*/update employee set salary=5000;
/*将姓名为’zs’的员工薪水修改为3000元*/
update employee set salary = 3000 where name='zs';
/*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 name='aaa';
/*将lisi的薪水在原有基础上增加1000元*/
update employee set salary = salary+1000 where name='lisi';
6.查询表中数据:
/*查询表中所有学生的信息*/select id,name,chinese,english,math 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;
在所有学生分数上加10分特长分*/
select name,(chinese+english+math)+10 from student;
/*统计每个学生的总分*/
select name,(chinese+english+math) from student;
/*使用别名表示学生分数*/
select name,(chinese+english+math) as 总分 from student;
/*使用别名表示学生分数,可以不用as*/
select name,(chinese+english+math) 总分 from student;
/*查询姓名为张三的学生成绩*/
select * from student where name='张三';
/*查询英语成绩大于90分的同学*/
select * from student where english>'90';
/*查询总分大于200分的所有同学*/
select name,(chinese+english+math) 总分 from student where chinese+english+math>200;
/*查询英语分数在 80－90之间的同学*/
select * from student where english>=80 and english=<90;
select * 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=89 or math=90 or math=91;
select * from student where math in(89,90,91);
/*查询所有姓李的学生成绩*/
select * from student where name like '李%';
select * from student where name like '李_';
/*查询数学分>80，语文分>80的同学*/
select * from student where math>80 and chinese>80;
select * from student where chinese is null;
/*对数学成绩排序（降序：从高到低，desc）后输出。*/
select name,math from student order by math desc;
/*对数学成绩排序（升序：从低到高，asc）后输出。*/
select name,math from student order by math asc;
/*对总分排序后输出，然后再按从高到低的顺序输出*/
select name,math+english+chinese from student order by math+english+chinese desc;
/*对姓李的学生成绩排序输出*/
select name,math+english+chinese from student where name like '李%' order by math+english+chinese desc;
/*统计一个班级共有多少学生*/
select count(*) from student;
select count(id) from student;
/*统计数学成绩大于80的学生人数*/
select count(*) from student where math>80;
/*统计总分大于250的人数*/
select count(*) from student where math+english+chinese>250;
/*细节 null不能被count*/
select count(chinese) from student;
/*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s*/
elect sum(math),sum(english),sum(chinese) from student;
/*统计一个班级语文、英语、数学的成绩总和*/
select sum(math+english+chinese) from student;
/*统计一个班级语文成绩平均分*/
select sum(chinese)/count(*) 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（数值范围在统计中特别有用）*/
select max(math+english+chinese) from student;
select min(math+english+chinese) from student;
/*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,sum(price) from orders group by product having sum(price)>100;
四、表约束
1.定义主键约束:
create table demo1(id int primary key,
name varchar(40)
);
2.插入空id:
insert into demo1(name) values('aaa');/*报错，主键不能为空*/3.插入重复的id:
insert into demo1(id,name) values(1,'aaa');/*报错，主键不能重复*/
insert into demo1(id,name) values(1,'aaa');
4.显定义主键自动增长(auto_increment):
create table demo2(id int auto_increment primary key,
name varchar(40)
);
5.定义唯一约束(unique):
create table demo3(id int auto_increment primary key,
name varchar(40) unique /*unique:唯一约束*/
);
6.定义非空(not null):
create table demo4(id int auto_increment primary key,
name varchar(40) not null
);
7.定义外键约束():
create table department(id int auto_increment primary key,
name varchar(30) not null
);
create table employee2(
id int auto_increment primary key,
name varchar(30) not null,
salary double,
department_id int,
/*外键约束*/
constraint department_id_FK foreign key(department_id) references department(id)
);
6.定义非空(not null):
create table demo4(id int auto_increment primary key,
name varchar(40) not null
);
7.删除主键:
alter table tablename drop primary key;