DDL：数据库定义语句
DML：增删改查
DCL：数据库控制语句
事物
数据库的表设计：
一、库操作
1.创建数据库
create database mydb1;
show databases;
2.创建带字符集的数据库
create database mydb2 CHARACTER SET=utf8;
show create database mydb2;
3.创建带校验的数据库
create database mydb3 CHARACTER SET=utf8 COLLATE utf8_general_ci;
4.显示数据库语句：SHOW DATABASES
5.显示数据库创建语句(详情) SHOW C
REATE DATABASE mydb3
6.数据库删除语句：
DROP DATABASE mydb3;
7.修改数据库的库字符编码
ALTER DATABASE mydb2 character set gb2312;
8.备份test库中的数据，并恢复（备份有一种方式，恢复有两种方式）
mysqldump -u root -p mydb2>c://test.sql 是一个win命令
第一种方式：
1.创建库
create database mydb2;
use mydb2;
2.恢复数据
source c://test.sql;
第二种方式：win命令
1.创建库
create database mydb2;
use mydb2;
exit;
2.恢复数据
mysql -u root -p mydb2<c://test.sql
9.创建表
1)create table test
(
name varchar(40)
);
2)增加数据
insert into test values("aaa");
二、表操作
1.创建数据库表
create table employee
(
id int,
name varchar(40),
sex char(4),
birthday date,
Entry_date date,
job varchar(100),
salary Decimal(8,2),
resume Text
);
2.在上面员工表的基本上增加一个image列。
alter table employee add image blob;3.修改job列，使其长度为60。
alter table employee modify job varchar(60);
4.删除sex列。
alter table employee drop image;
5.表名改为user。
rename table employee to user;
6.修改表的字符集为utf-8alter table user character set gbk;
alter table user character set utf8;
7.列名name修改为username
删除表
alter table user change column name username varchar(100);
8.删除表
drop table user;
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(null,null,'male','1993-03-04','2016-11-10','1000','i am a developer');
//无法插入
insert into employee values('male','1993-03-04','2016-11-10','1000','i am a developer');
//可以包起来所有类型
insert into employee values('5',null,'male','1993-03-04','2016-11-10','1000','i am a developer');
//指定某些列插入数据
insert into employee(id) values(6);
//插入汉字
insert into employee(id,name) values(6,'张三');
要告诉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');
要想查看时不乱码
show variables like 'chara%';
set character_set_results=gb2312;
select * from employee;
2.修改表数据
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='zhangsan';
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='张三';
将wu的薪水在原有基础上增加1000元。
update employee set salary = salary+1000 where name='张三';
3.删除
删除表中名称为’zs’的记录。
delete from employee where job='ccc';
删除表中所有记录。
delete from employee;
使用truncate删除表中记录
truncate table employee;
//细节
delete from employee where
4.查询
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;
//可以不用as
select name,(chinese+english+math) 总分 from student;
查询姓名为wu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;
对数学成绩排序后输出。
select name,math from student order by math desc;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的学生有多少个？
select count(*) from student where math>80;
统计总分大于250的人数有多少？
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select 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(chinese) 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)
);
//1.插入空id
insert into demo1(name) values('aaa');
//2.不允许重复
insert into demo1(id,name) values(1,'aaa');
insert into demo1(id,name) values(1,'aaa');
2.定义主键自动增长
create table demo2(
id int auto_increment primary key,
name varchar(40)
);
insert into demo2(name) values('aaa');
delete from demo2 where id = 3;
3.定义唯一约束
create table demo3(
id int auto_increment primary key,
name varchar(40) unique
);
insert into demo3(name) values('aaa');
4.定义非空
create table demo4(
id int auto_increment primary key,
name varchar(40) not null
);
insert into demo3(password) values('123');
5.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,
constraint department_id_FK foreign key(department_id) references department(id)
);
