mysql学习笔记基础命令

mysql数据库

关系数据库

SQL结构化查询语言，

socket介绍 root root

DDL：数据定义语言

DML：(data Manioulation)数据操作语言

DCL：(data control language)数据控制语言

DQL：(data Qiery language)数据查询语言 (重点)

docket连接软件。

tcp和udp协议：

tcp安全连接：建立连接，三次握手，（文件传输使用tcp 安全性，传输效率低）

udp不安全连接：直接向目的地址发送信息，可以不建立连接，可能丢失信息。（游戏使用udp）

1.DCL:（不重要）

创建用户，用户只能在指定ip地址

create user 用户名@IP地址 identified by '密码'

create user  root@'%' identified by 'root'    //%表示所有的ip地址都适用

给用户授权，所有权限可以用all代替。

grant 权限1，……权限n on 数据库.* to 用户名@IP地址

撤销权限

revoke

查看权限

show grants for 用户名

删除用户

drop user 用户名@ip地址

2.DDL语言，对数据库和表结构进行操作

MYSQL数据类型	含义
time
data
datatime	8字节，日期时间
timestamp	4字节，自动存储修改记录的时间
year	1字节，年份

整型，浮点型，字符串数据类型（char：固定长度, varchar:可变长度），

操作数据库

查看数据库 show database

使用数据库

创建数据库并指定编码

CREATE DATABASE test DEFAULT CHARACTER SET utf8

创建表 create table 表名{}

create table student(id int primary keyname varchar(20)age tinyint unsignedgander char(1)
);

查看当前数据库中的表

查看表结构 dese 表名

删除表 drop 表名

修改表：

添加列

alter table 表名 add(列名 类类型……);

修改列类型

alter table student modify hobby int

修改表的列名称和类型

alter table 表名 change 原列名 新列名 列名类型

删除列

alter table student drop newhobby

修改表名

ALTER TABLE STUDENT RENAME TO STU

3.DML 数据操作语言，语法(增删改)

插入数据（一次插入就是一行）

insert into 表名（列名1，列名2，列名3） values（列值1，列值2，列值3）;

修改记录

update stu set age=22;   //修改表中的所有age为22

update stu set age=23,name="zhangsan" where id =1;   //只修改id为1的数据

删除数据

delete from stu where id =2;

关闭防火墙：

systemctl status firewalld
systemctl stop firewalld
systemctl disable firewalld

表约束

约束名称	描述
NOT NULL	非空约束
UNIQUE	唯一约束
PRIMARY KEY	主键约束
FOREIGN KEY	外键约束（关键字）
DEFAULT	默认值（缺省值）

mysql -uroot -proot

create database mydatabase charset utf8

create table author(
aut_id int unique,    //添加非空约束
aut_name char
)插入数据
insert into anthor(aut_id) values (2);
查看表
select * from author;
删除表
drop table author;
创建一个新表
create table author(aut_id int,
aut_name char (4) default '小白'   //添加默认属性)
create table author (
aut_id int primary key,      //添加主键约束
aut_name char (4) default '小白'
)
//auto_increment   主键自增约束
create table author(
aut_id int primary key auto_increment,
aut_name char(4)
)
查看表
select * from author
FOREIGN KEY  约束
外键可以建立多个，
1.删除表时，如果不删除引用外键的表，被引用的表不能直接删除
2.外键的值必须来源于引用的表的主键字段
create table book(
book_id int primary key,
book_name char (20) not null,
aut_id int ,
foreign key( aut_id) reference author(aut_id)  //外键从作者表中传入
);
如果作者表中没有id为2的作者，那么author_id = 2 的书籍信息不能插入book表

可视化操作数据库

//创建数据库以及创建表单
drop table if exists student;
create table student(
id int(10) primary key,
name varchar(10),
age int (10) not null,gander varchar (2)
);drop table if exists course;
create table course (
id int (10) primary key,name varchar(10),t_id int (10)
);drop table if exists teacher;
create table teacher(id int (10) primary key,name varchar(10)
);drop table if exists scores;
create table scores(s_id int ,score int(10),c_id int (10),primary key (s_id,c_id)
);

表单填充数据

insert into student(id,name,age,gender)values (1,'baijie',19,'男');
insert into student(id,name,age,gender)values (1,'鲢鱼',19,'男');
insert into student(id,name,age,gender)values (1,'志伟',19,'男');
insert into student(id,name,age,gender)values (1,'李星',19,'男');
insert into student(id,name,age,gender)values (1,'张琪',19,'女');
insert into student(id,name,age,gender)values (1,'吴三',19,'女');
insert into student(id,name,age,gender)values (1,'张倩',19,'女');insert into course(id,name,t_id)values(1,'数学',1);
insert into course(id,name,t_id)values(2,'语文',2);
insert into course(id,name,t_id)values(3,'c++',3);
insert into course(id,name,t_id)values(4,'java',4);insert into teacher (id,name)values (1,'张楠');
insert into teacher (id,name)values (1,'老孙');
insert into teacher (id,name)values (1,'微微');
insert into teacher (id,name)values (1,'磊哥');
insert into teacher (id,name)values (1,'慧姐');insert into scores (s_id,score,c_id)values(1,80,1);
insert into scores (s_id,score,c_id)values(1,56,2);
insert into scores (s_id,score,c_id)values(1,95,3);
insert into scores (s_id,score,c_id)values(1,49,4);
insert into scores (s_id,score,c_id)values(1,76,5);insert into scores (s_id,score,c_id)values(2,35,1);
insert into scores (s_id,score,c_id)values(2,86,2);
insert into scores (s_id,score,c_id)values(2,73,3);
insert into scores (s_id,score,c_id)values(2,56,4);
insert into scores (s_id,score,c_id)values(2,78,5);insert into scores (s_id,score,c_id)values(3,64,2);
insert into scores (s_id,score,c_id)values(3,93,3);
insert into scores (s_id,score,c_id)values(3,90,4);
insert into scores (s_id,score,c_id)values(3,83,5);insert into scores (s_id,score,c_id)values(4,77,1);
insert into scores (s_id,score,c_id)values(4,99,2);
insert into scores (s_id,score,c_id)values(4,66,3);insert into scores (s_id,score,c_id)values(5,83,2);
insert into scores (s_id,score,c_id)values(5,92,3);
insert into scores (s_id,score,c_id)values(5,73,4);insert into scores (s_id,score,c_id)values(6,77,1);
insert into scores (s_id,score,c_id)values(6,38,2);
insert into scores (s_id,score,c_id)values(6,88,3);
insert into scores (s_id,score,c_id)values(6,55,4);
insert into scores (s_id,score,c_id)values(6,75,5);insert into scores (s_id,score,c_id)values(7,39,1);
insert into scores (s_id,score,c_id)values(7,83,2);
insert into scores (s_id,score,c_id)values(7,75,3);
insert into scores (s_id,score,c_id)values(7,54,4);
insert into scores (s_id,score,c_id)values(7,73,5);insert into scores (s_id,score,c_id)values(8,83,2);
insert into scores (s_id,score,c_id)values(8,76,3);
insert into scores (s_id,score,c_id)values(8,66,4);
insert into scores (s_id,score,c_id)values(8,74,5);insert into scores (s_id,score,c_id)values(9,30,1);
insert into scores (s_id,score,c_id)values(9,80,2);
insert into scores (s_id,score,c_id)values(9,71,3);
insert into scores (s_id,score,c_id)values(9,70,5);insert into scores (s_id,score,c_id)values(10,80,2);
insert into scores (s_id,score,c_id)values(10,70,3);
insert into scores (s_id,score,c_id)values(10,59,4);
insert into scores (s_id,score,c_id)values(10,79,5);

单表查询

查询所有列    select * from 表名;
查询指定列    select id ,name from student;
** 完全重复的记录只显示一次   在查询的列前面+ distinct
列运算：数据类型可以进行加减乘除，字符类型可以进行连接运算
** 起别名：
select s_id as student_id from scores;    别名为：student_idselect s_id as student_id from scores as s;   给表起别名条件控制：
select * from teacher where id=2;     大于小于等于
select * from teacher where id in (1,2,5);模糊查询，
select * from teacher where name like '%jie%'

模糊查询：https://www.cnblogs.com/muzixiaodan/p/5583473.html

排序：asc正序排列，desc倒序排列
select * from student order by age asc;

聚合函数：
count:select count (列名) from 表名;
max:select max (列名) from 表名;
min:select min (列名) from 表名;
sum:select sum (列名) from 表名;
avg:select avg (列名) from 表名;

分组和limit   group by...having select 分组列名，聚合函数1，聚合函数2 from 表名 group by 该分组名;group by和 where 的区别
where是先筛选条件，group by是先进行分组，再根据having后的条件进行筛选limit（mysql中独有的语法）
例子： select * from student limit 1,2;     表示从第一行中查2行（用于分页）

union和union all
将查询后的数据放在一起
select id,name from teacher unionunion 和union all的区别：union只筛选一个，union all 可连接重复的数据
连接多个不同表的联合查询
select id name from student
union all
select id name name from teacher