mysql基础

1. 关系型数据库介绍

1.1 数据结构模型

数据结构模型主要有：

• 层次模型
• 网状结构
• 关系模型

关系模型： 二维关系：row，column

数据库管理系统：DBMS 关系：Relational，RDBMS

1.2 RDBMS专业名词

常见的关系型数据库管理系统：

• MySQL：MySQL，MariaDB，Percona-Server
• PostgreSQL：简称为pgsql
• Oracle
• MSSQL

事务：多个操作被当作一个整体对待就称为一个事务 要看一个关系型数据库是否支持事务，需要看其是否支持并满足ACID测试 ACID：ACID是事务的一个基本标准

• A：Automicity，原子性
• C：Consistency，一致性
• I：Isolation，隔离性
• D：Durability，持久性

如果你对ACID感兴趣，可以查看这里了解详细说明，ACID将不作为我们讲解的重点。

SQL：Structure Query Language，结构化查询语言

约束：constraint，向数据表提供的数据要遵守的限制

• 主键约束：一个或多个字段的组合，填入的数据必须能在本表中唯一标识本行。且必须提供数据，不能为空（NOT NULL）。 一个表只能存在一个
• 惟一键约束：一个或多个字段的组合，填入的数据必须能在本表中唯一标识本行。允许为空（NULL） 一个表可以存在多个
• 外键约束：一个表中的某字段可填入数据取决于另一个表的主键已有的数据
• 检查性约束

索引：将表中的一个或多个字段中的数据复制一份另存，并且这些数据需要按特定次序排序存储

关系运算：

• 选择：挑选出符合条件的行（部分行）
• 投影：挑选出需要的字段
• 连接

数据抽象方式：

• 物理层：决定数据的存储格式，即RDBMS在磁盘上如何组织文件
• 逻辑层：描述DB存储什么数据，以及数据间存在什么样的关系
• 视图层：描述DB中的部分数据

1.3 关系型数据库的常见组件

关系型数据库的常见组件有：

• 数据库：database
• 表：table，由行（row）和列（column）组成
• 索引：index
• 视图：view
• 用户：user
• 权限：privilege
• 存储过程：procedure
• 存储函数：function
• 触发器：trigger
• 事件调度器：event scheduler

1.4 SQL语句

SQL语句有三种类型：

• DDL：Data Defination Language，数据定义语言
• DML：Data Manipulation Language，数据操纵语言
• DCL：Data Control Language，数据控制语言

SQL语句类型	对应操作
DDL	CREATE：创建 DROP：删除 ALTER：修改
DML	INSERT：向表中插入数据建 DELETE：删除表中数据 UPDATE：更新表中数据 SELECT：查询表中数据
DCL	GRANT：授权 REVOKE：移除授权

2. mysql安装与配置

2.1 mysql安装

mysql安装方式有三种：

• 源代码：编译安装
• 二进制格式的程序包：展开至特定路径，并经过简单配置后即可使用
• 程序包管理器管理的程序包：
  • rpm：有两种
    • OS Vendor：操作系统发行商提供的
    • 项目官方提供的
  • deb

 

//配置mysql的yum源
[root@20liuzhenchao ~]# cd /usr/local/
[root@20liuzhenchao local]# wget http://dev.mysql.com/get/mysql57-community-release-el7-10.noarch.rpm
下载过程略
[root@20liuzhenchao local]# ls
apache  apr  apr-util  bin  etc  games  include  lib  lib64  libexec  mysql57-community-release-el7-10.noarch.rpm  nginx  php  sbin  share  src
[root@20liuzhenchao local]# yum -y install mysql57-community-release-el7-10.noarch.rpm
Loaded plugins: fastestmirror, product-id, search-disabled-repos, subscription-
              : manager
This system is not registered with an entitlement server. You can use subscription-manager to register.
Examining mysql57-community-release-el7-10.noarch.rpm: mysql57-community-release-el7-10.noarch 
....
Installed:
  mysql57-community-release.noarch 0:el7-10

Complete!
[root@20liuzhenchao local]# ls /etc/yum.repos.d/
CentOS7-Base-163.repo  epel.repo  epel.repo.rpmnew  epel-testing.repo  myrepo.repo  mysql-community.repo  mysql-community-source.repo  redhat.repo

//安装mysql5.7
[root@20liuzhenchao local]# yum -y install mysql-community-server.x86_64 mysql-community-client.i686 mysql-community-common.x86_64 mysql-community-devel.x86_64
Loaded plugins: fastestmirror, product-id, search-disabled-repos, subscription-
              : manager
This system is not registered with an entitlement server. You can use subscription-manager to register.
Loading mirror speeds from cached hostfile
Resolving Dependencies
--> Running transaction check
---> Package mysql-community-client.x86_64 0:5.7.23-1.el7 will be installed
--> Processing Dependency: mysql-community-libs(x86-64) >= 5.7.9 for package: mysql-community-client-5.7.23-1.el7.x86_64 
....
Installed:
  mysql-community-client.x86_64 0:5.7.23-1.el7
  mysql-community-common.x86_64 0:5.7.23-1.el7
  mysql-community-devel.x86_64 0:5.7.23-1.el7
  mysql-community-libs.x86_64 0:5.7.23-1.el7
  mysql-community-libs-compat.x86_64 0:5.7.23-1.el7
  mysql-community-server.x86_64 0:5.7.23-1.el7

Replaced:
  mariadb-libs.x86_64 1:5.5.56-2.el7

Complete!

2.2 mysql配置

//启动mysql
[root@20liuzhenchao ~]# systemctl start mysqld
[root@20liuzhenchao ~]# systemctl status mysqld
● mysqld.service - MySQL Server
   Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled)
   Active: active (running) since 一 2019-04-22 14:18:23 CST; 1min 29s ago
     Docs: man:mysqld(8)
           http://dev.mysql.com/doc/refman/en/using-systemd.html
  Process: 13899 ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid $MYSQLD_OPTS (code=exited, status=0/SUCCESS)
  Process: 13823 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, status=0/SUCCESS)
 Main PID: 13902 (mysqld)
   CGroup: /system.slice/mysqld.service
           └─13902 /usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid

4月 22 14:18:19 20liuzhenchao systemd[1]: Starting MySQL Server...
4月 22 14:18:23 20liuzhenchao systemd[1]: Started MySQL Server.

//确保3306端口已经监听起来
[root@20liuzhenchao ~]# ss -antl |grep 3306
LISTEN     0      80          :::3306                    :::*  

//在日志文件中找出临时密码
[root@20liuzhenchao ~]# grep "password" /var/log/mysqld.log 
2019-04-22T06:18:21.008637Z 1 [Note] A temporary password is generated for root@localhost: LIUPk=c3)Tp<
//此处的临时密码为LIUPk=c3)Tp<

//使用获取到的临时密码登录mysql
[root@20liuzhenchao ~]# mysql -uroot -p
Enter password:     //此处输入密码，可以直接复制你的密码粘贴至此处，也可手动输入
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.7.25

Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql>       //看到有这样的标识符则表示成功登录了

//修改mysql登录密码
mysql> set global validate_password_policy=0;
Query OK, 0 rows affected (0.00 sec)

mysql> set global validate_password_length=1;
Query OK, 0 rows affected (0.00 sec)

mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY '123456';
Query OK, 0 rows affected (0.01 sec)

mysql> quit
Bye

//为避免mysql自动升级，这里需要卸载最开始安装的yum源
[root@20liuzhenchao ~]# rpm -qa |grep mysql
mysql-community-devel-5.7.25-1.el7.x86_64
mysql-community-libs-5.7.25-1.el7.i686
mysql-community-server-5.7.25-1.el7.x86_64
mysql-community-common-5.7.25-1.el7.x86_64
mysql-community-libs-compat-5.7.25-1.el7.x86_64
mysql-community-common-5.7.25-1.el7.i686
mysql-community-client-5.7.25-1.el7.x86_64
mysql-community-libs-5.7.25-1.el7.x86_64
mysql57-community-release-el7-10.noarch
[root@20liuzhenchao ~]# yum -y remove mysql57-community-release-el7-10.noarch
已加载插件：fastestmirror, product-id, search-disabled-repos, subscription-manager
This system is not registered with an entitlement server. You can use subscription-manager to register.
正在解决依赖关系
--> 正在检查事务
---> 软件包 mysql57-community-release.noarch.0.el7-10 将被 删除
--> 解决依赖关系完成

安装大小：30 k
Downloading packages:
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  正在删除    : mysql57-community-release-el7-10.noarch                                                                                              1/1 
Loading mirror speeds from cached hostfile
  验证中      : mysql57-community-release-el7-10.noarch                                                                                              1/1 

删除:
  mysql57-community-release.noarch 0:el7-10         
完毕！

3. mysql的程序组成

• 客户端
  • mysql：CLI交互式客户端程序
  • mysql_secure_installation：安全初始化，强烈建议安装完以后执行此命令
  • mysqldump：mysql备份工具
  • mysqladmin
• 服务器端
  • mysqld

3.1 mysql工具使用

//语法：mysql [OPTIONS] [database]
//常用的OPTIONS：
    -uUSERNAME      //指定用户名，默认为root
    -hHOST          //指定服务器主机，默认为localhost，推荐使用ip地址
    -pPASSWORD      //指定用户的密码
    -P#             //指定数据库监听的端口，这里的#需用实际的端口号代替，如-P3307
    -V              //查看当前使用的mysql版本
    -e          //不登录mysql执行sql语句后退出，常用于脚本


[root@20liuzhenchao ~]# mysql -V
mysql  Ver 14.14 Distrib 5.7.25, for Linux (x86_64) using  EditLine wrapper

[root@20liuzhenchao ~]# mysql -uroot -p123456 -h127.0.0.1
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 7
Server version: 5.7.25 MySQL Community Server (GPL)

Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> 


//注意，不推荐直接在命令行里直接用-pPASSWORD的方式登录，而是使用-p选项，然后交互式输入密码
[root@20liuzhenchao ~]# mysql -uroot -p -h127.0.0.1
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 5.7.25 MySQL Community Server (GPL)

Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql>  

[root@20liuzhenchao ~]# mysql -uroot -p -h127.0.0.1 -e 'SHOW DATABASES;'
Enter password: 
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+

3.2 服务器监听的两种socket地址

socket类型	说明
ip socket	默认监听在tcp的3306端口，支持远程通信
unix sock	监听在sock文件上（/tmp/mysql.sock，/var/lib/mysql/mysql.sock）仅支持本地通信 server地址只能是：localhost，127.0.0.1

4. mysql数据库操作

4.1 DDL操作

4.1.1 数据库操作

//创建数据库
//语法：CREATE DATABASE [IF NOT EXISTS] 'DB_NAME';
//创建数据库liuzhenchao
mysql> CREATE DATABASE IF NOT EXISTS liuzhenchao;
Query OK, 1 row affected (0.00 sec)

//查看当前实例有哪些数据库
mysql> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| liuzhenchao        |
| mysql              |
| performance_schema |
| sys                |
+--------------------+

5 rows in set (0.00 sec)

//删除数据库
//语法：DROP DATABASE [IF EXISTS] 'DB_NAME';
//删除数据库liuzhenchao
mysql> DROP DATABASE IF EXISTS liuzhenchao;
Query OK, 0 rows affected (0.00 sec)

mysql> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0.00 sec)

4.1.2 表操作

//创建表
//语法：CREATE TABLE table_name (col1 datatype 修饰符,col2 datatype 修饰符) ENGINE='存储引擎类型';
//在数据库liuzhenchao里创建表liu
mysql> CREATE DATABASE liuzhenchao;
      //创建数据库liuzhenchao
Query OK, 1 row affected (0.00 sec)

mysql> use liuzhenchao;      //进入liuzhenchao数据库
Database changed
mysql> CREATE TABLE liu (id int NOT NULL,name VARCHAR(100) NOT NULL,age tinyint);      //创建liu表
Query OK, 0 rows affected (0.01 sec)


//查看当前数据库有哪些表
mysql> show tables;
+-----------------------+
| Tables_in_liuzhenchao |
+-----------------------+
| liu                   |
+-----------------------+
1 row in set (0.00 sec)

//删除表
//语法：DROP TABLE [ IF EXISTS ] 'table_name';
//删除表liu
mysql> drop table liu;
Query OK, 0 rows affected (0.01 sec)

mysql> show tables;
Empty set (0.00 sec)

4.1.3 用户操作

mysql用户帐号由两部分组成，如'USERNAME'@'HOST'，表示此USERNAME只能从此HOST上远程登录 这里（'USERNAME'@'HOST'）的HOST用于限制此用户可通过哪些主机远程连接mysql程序，其值可为：

• IP地址，如：172.16.12.129
• 通配符
  • %：匹配任意长度的任意字符，常用于设置允许从任何主机登录
  • _：匹配任意单个字符

 

//数据库用户创建
//语法：CREATE USER 'username'@'host' [IDENTIFIED BY 'password'];
//创建数据库用户liuzhenchao
mysql> create user 'liuzhenchao'@'127.0.0.1' identified by '123456';
Query OK, 0 rows affected (0.01 sec)

//使用新创建的用户和密码登录
[root@20liuzhenchao ~]# mysql -uliuzhenchao -p123456 -h127.0.0.1
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 11
Server version: 5.7.25 MySQL Community Server (GPL)

Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> 


//删除数据库用户
//语法：DROP USER 'username'@'host'; 
mysql> drop user 'liuzhenchao'@'127.0.0.1';
Query OK, 0 rows affected (0.00 sec)

4.1.4 查看命令SHOW

mysql> SHOW CHARACTER SET;      //查看支持的所有字符集
+----------+---------------------------------+---------------------+--------+
| Charset  | Description                     | Default collation   | Maxlen |
+----------+---------------------------------+---------------------+--------+
| big5     | Big5 Traditional Chinese        | big5_chinese_ci     |      2 |
| dec8     | DEC West European               | dec8_swedish_ci     |      1 |
| cp850    | DOS West European               | cp850_general_ci    |      1 |
| hp8      | HP West European                | hp8_english_ci      |      1 |
| koi8r    | KOI8-R Relcom Russian           | koi8r_general_ci    |      1 |
| latin1   | cp1252 West European            | latin1_swedish_ci   |      1 | 
......
......

mysql> SHOW ENGINES;        //查看当前数据库支持的所有存储引擎
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine             | Support | Comment
                 | Transactions | XA   | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| InnoDB             | DEFAULT | Supports transactions, row-level locking, and
foreign keys     | YES          | YES  | YES        |
| MRG_MYISAM         | YES     | Collection of identical MyISAM tables
                 | NO           | NO   | NO         |
| MEMORY             | YES     | Hash based, stored in memory, useful for temporary tables      | NO           | NO   | NO         |
| BLACKHOLE          | YES     | /dev/null storage engine (anything you write to it disappears) | NO           | NO   | NO         |
| MyISAM             | YES     | MyISAM storage engine                                          | NO           | NO   | NO         |
| CSV                | YES     | CSV storage engine                                            | NO           | NO   | NO         |
| ARCHIVE            | YES     | Archive storage engine                                        | NO           | NO   | NO         |
| PERFORMANCE_SCHEMA | YES     | Performance Schema                                            | NO           | NO   | NO         |
| FEDERATED          | NO      | Federated MySQL storage engine                                | NULL         | NULL | NULL       |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
9 rows in set (0.00 sec)

mysql> show databases;  //查看数据库信息
+--------------------+
| Database           |
+--------------------+
| information_schema |
| liuzhenchao        |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

mysql> show tables from liuzhenchao;
//不进入某数据库而列出其包含的所有表
+-----------------------+
| Tables_in_liuzhenchao |
+-----------------------+
| liu                   |
+-----------------------+
1 row in set (0.00 sec)

//查看表结构
//语法：DESC [db_name.]table_name;
mysql> desc liuzhenchao.liu;
+--------------+-------------+------+-----+---------+-------+
| Field        | Type        | Null | Key | Default | Extra |
+--------------+-------------+------+-----+---------+-------+
| id           | int(11)     | NO   |     | NULL    |       |
| name         | varchar(50) | YES  |     | NULL    |       |
| phone_numble | varchar(11) | YES  |     | NULL    |       |
+--------------+-------------+------+-----+---------+-------+
3 rows in set (0.07 sec)

//查看某表的创建命令
//语法：SHOW CREATE TABLE table_name;
mysql> show create table liuzhenchao.liu;
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                      |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| liu   | CREATE TABLE `liu` (
  `id` int(11) NOT NULL,
  `name` varchar(50) DEFAULT NULL,
  `phone_numble` varchar(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

//查看某表的状态
//语法：SHOW TABLE STATUS LIKE 'table_name'\G
mysql> use liuzhenchao;      //进入数据库liuzhenchao
Database changed
mysql> show table status like 'liu'\G
//查看liu表的状态
*************************** 1. row ***************************
           Name: liu
         Engine: InnoDB
        Version: 10
     Row_format: Dynamic
           Rows: 0
 Avg_row_length: 0
    Data_length: 16384
Max_data_length: 0
   Index_length: 0
      Data_free: 0
 Auto_increment: NULL
    Create_time: 2019-04-23 14:45:56
    Update_time: NULL
     Check_time: NULL
      Collation: latin1_swedish_ci
       Checksum: NULL
 Create_options: 
        Comment: 
1 row in set (0.00 sec)

4.1.5 获取帮助

//获取命令使用帮助
//语法：HELP keyword;
mysql> HELP CREATE TABLE;       //获取创建表的帮助
Name: 'CREATE TABLE'
Description:
Syntax:
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    (create_definition,...)
    [table_options]
    [partition_options]

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    [(create_definition,...)]
    [table_options]
    [partition_options]
    [IGNORE | REPLACE]
    [AS] query_expression
 ......
 ......

4.2 DML操作

DML操作包括增(INSERT)、删(DELETE)、改(UPDATE)、查(SELECT)，均属针对表的操作。

4.2.1 INSERT语句

//DML操作之增操作insert
//语法：INSERT [INTO] table_name [(column_name,...)] {VALUES | VALUE} (value1,...),(...),...

mysql> use liuzhenchao;
Database changed
mysql> insert into liu(id,name,phone_numble) value(1,'tom',13297040973);
Query OK, 1 row affected (0.00 sec)      //一次插入一条记录
Query OK, 1 row affected (0.01 sec)

mysql> insert into liu values(2,'jerry',33333333333),(3,'zhen',44444444444),(4,'chao',55555555555),(5,'boss',19045045021);
//一次插入多条记录
Query OK, 4 rows affected (0.00 sec)

4.2.2 SELECT语句

字段column表示法

表示符	代表什么？
*	所有字段
as	字段别名，如col1 AS alias1 当表名很长时用别名代替

条件判断语句WHERE

操作类型	常用操作符
操作符	>，<，>=，<=，=，!= BETWEEN column# AND column# LIKE：模糊匹配 RLIKE：基于正则表达式进行模式匹配 IS NOT NULL：非空 IS NULL：空
条件逻辑操作	AND OR NOT

ORDER BY：排序，默认为升序（ASC）

ORDER BY语句	意义
ORDER BY ‘column_name'	根据column_name进行升序排序
ORDER BY 'column_name' DESC	根据column_name进行降序排序
ORDER BY ’column_name' LIMIT 2	根据column_name进行升序排序 并只取前2个结果
ORDER BY ‘column_name' LIMIT 1,2	根据column_name进行升序排序

并且略过第1个结果取后面的2个结果

//DML操作之查操作select
//语法：SELECT column1,column2,... FROM table_name [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n];

mysql> use liuzhenchao;
Database changed
mysql> select * from liu;
+----+-------+--------------+
| id | name  | phone_numble |
+----+-------+--------------+
|  1 | tom   | 13297040973  |
|  2 | jerry | 33333333333  |
|  3 | zhen  | 44444444444  |
|  4 | chao  | 55555555555  |
|  5 | boss  | 19045045021  |
+----+-------+--------------+
5 rows in set (0.00 sec)

mysql> select name from liu;
+-------+
| name  |
+-------+
| tom   |
| jerry |
| zhen  |
| chao  |
| boss  |
+-------+
5 rows in set (0.00 sec)

mysql> alter table liu add column age tinyint(4) not null;
Query OK, 0 rows affected (1.72 sec)
//插入一列age
mysql> desc liuzhenchao.liu;
+--------------+-------------+------+-----+---------+-------+
| Field        | Type        | Null | Key | Default | Extra |
+--------------+-------------+------+-----+---------+-------+
| id           | int(11)     | NO   |     | NULL    |       |
| name         | varchar(50) | YES  |     | NULL    |       |
| phone_numble | varchar(11) | YES  |     | NULL    |       |
| age          | tinyint(4)  | NO   |     | NULL    |       |
+--------------+-------------+------+-----+---------+-------+
mysql> update liu set age = 23 where id =1;
Query OK, 1 row affected (0.00 sec)

mysql> update liu set age = 30 where id =2;
Query OK, 1 row affected (0.00 sec)

mysql> update liu set age = 60 where id =3;
Query OK, 1 row affected (0.01 sec)

mysql> update liu set age = 80 where id =4;
Query OK, 1 row affected (0.00 sec)

mysql> update liu set age = 12 where id =5;
Query OK, 1 row affected (0.00 sec)
//向age列中分别插入数据

mysql> select * from liu order by age;
+----+-------+--------------+-----+
| id | name  | phone_numble | age |
+----+-------+--------------+-----+
|  5 | boss  | 19045045021  |  12 |
|  1 | tom   | 13297040973  |  23 |
|  2 | jerry | 33333333333  |  30 |
|  3 | zhen  | 44444444444  |  60 |
|  4 | chao  | 55555555555  |  80 |
+----+-------+--------------+-----+
5 rows in set (0.00 sec)

mysql> select * from liu order by age desc;
+----+-------+--------------+-----+
| id | name  | phone_numble | age |
+----+-------+--------------+-----+
|  4 | chao  | 55555555555  |  80 |
|  3 | zhen  | 44444444444  |  60 |
|  2 | jerry | 33333333333  |  30 |
|  1 | tom   | 13297040973  |  23 |
|  5 | boss  | 19045045021  |  12 |
+----+-------+--------------+-----+
5 rows in set (0.00 sec)
//按年龄降序排列

mysql> select * from liu order by age desc limit 2;
+----+------+--------------+-----+
| id | name | phone_numble | age |
+----+------+--------------+-----+
|  4 | chao | 55555555555  |  80 |
|  3 | zhen | 44444444444  |  60 |
+----+------+--------------+-----+
2 rows in set (0.00 sec)
//排列后取前两个数据

mysql> select * from liu order by age desc limit 1,2;
+----+-------+--------------+-----+
| id | name  | phone_numble | age |
+----+-------+--------------+-----+
|  3 | zhen  | 44444444444  |  60 |
|  2 | jerry | 33333333333  |  30 |
+----+-------+--------------+-----+
2 rows in set (0.00 sec)
//跳过第一个数据后取前两个

mysql> select * from liu where age >=30;
+----+-------+--------------+-----+
| id | name  | phone_numble | age |
+----+-------+--------------+-----+
|  2 | jerry | 33333333333  |  30 |
|  3 | zhen  | 44444444444  |  60 |
|  4 | chao  | 55555555555  |  80 |
+----+-------+--------------+-----+
3 rows in set (0.00 sec)

mysql> select * from liu where age >=30 and name = 'zhen';
+----+------+--------------+-----+
| id | name | phone_numble | age |
+----+------+--------------+-----+
|  3 | zhen | 44444444444  |  60 |
+----+------+--------------+-----+
1 row in set (0.00 sec)

mysql> select * from liu where age between 10 and 30;
+----+-------+--------------+-----+
| id | name  | phone_numble | age |
+----+-------+--------------+-----+
|  1 | tom   | 13297040973  |  23 |
|  2 | jerry | 33333333333  |  30 |
|  5 | boss  | 19045045021  |  12 |
+----+-------+--------------+-----+
3 rows in set (0.00 sec)

mysql> insert into liu(id,phone_numble,age) value(6,13080619342,55);
Query OK, 1 row affected (0.00 sec)
//加入一行name为空的记录

mysql> select * from liu where name is not null;
+----+-------+--------------+-----+
| id | name  | phone_numble | age |
+----+-------+--------------+-----+
|  1 | tom   | 13297040973  |  23 |
|  2 | jerry | 33333333333  |  30 |
|  3 | zhen  | 44444444444  |  60 |
|  4 | chao  | 55555555555  |  80 |
|  5 | boss  | 19045045021  |  12 |
+----+-------+--------------+-----+
5 rows in set (0.00 sec)

mysql> select * from liu where name is null;
+----+------+--------------+-----+
| id | name | phone_numble | age |
+----+------+--------------+-----+
|  6 | NULL | 13080619342  |  55 |
+----+------+--------------+-----+
1 row in set (0.00 sec)

4.2.3 update语句

//DML操作之改操作update
//语法：UPDATE table_name SET column1 = new_value1[,column2 = new_value2,...] [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n];

mysql> select * from liu;
+----+-------+--------------+-----+
| id | name  | phone_numble | age |
+----+-------+--------------+-----+
|  1 | tom   | 13297040973  |  23 |
|  2 | jerry | 33333333333  |  30 |
|  3 | zhen  | 44444444444  |  60 |
|  4 | chao  | 55555555555  |  80 |
|  5 | boss  | 19045045021  |  12 |
|  6 | NULL  | 13080619342  |  55 |
+----+-------+--------------+-----+
6 rows in set (0.01 sec)

mysql> update liu set age =40 where id =1;
Query OK, 1 row affected (0.00 sec)

mysql> select * from liu where id =1;
+----+------+--------------+-----+
| id | name | phone_numble | age |
+----+------+--------------+-----+
|  1 | tom  | 13297040973  |  40 |
+----+------+--------------+-----+
1 row in set (0.00 sec)

4.2.4 delete语句

//DML操作之删操作delete
//语法：DELETE FROM table_name [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n];

mysql> select * from liu;
+----+-------+--------------+-----+
| id | name  | phone_numble | age |
+----+-------+--------------+-----+
|  1 | tom   | 13297040973  |  40 |
|  2 | jerry | 33333333333  |  30 |
|  3 | zhen  | 44444444444  |  60 |
|  4 | chao  | 55555555555  |  80 |
|  5 | boss  | 19045045021  |  12 |
|  6 | NULL  | 13080619342  |  55 |
+----+-------+--------------+-----+
6 rows in set (0.00 sec)

mysql> delete from liu where id = 6;
//删除某条记录
Query OK, 1 row affected (0.00 sec)

mysql> select * from liu;
+----+-------+--------------+-----+
| id | name  | phone_numble | age |
+----+-------+--------------+-----+
|  1 | tom   | 13297040973  |  40 |
|  2 | jerry | 33333333333  |  30 |
|  3 | zhen  | 44444444444  |  60 |
|  4 | chao  | 55555555555  |  80 |
|  5 | boss  | 19045045021  |  12 |
+----+-------+--------------+-----+
5 rows in set (0.00 sec)

mysql> delete from liu;//删除整张表的内容
Query OK, 5 rows affected (0.00 sec)

mysql> select * from liu;
Empty set (0.00 sec)

mysql> desc liu;
+--------------+-------------+------+-----+---------+-------+
| Field        | Type        | Null | Key | Default | Extra |
+--------------+-------------+------+-----+---------+-------+
| id           | int(11)     | NO   |     | NULL    |       |
| name         | varchar(50) | YES  |     | NULL    |       |
| phone_numble | varchar(11) | YES  |     | NULL    |       |
| age          | tinyint(4)  | NO   |     | NULL    |       |
+--------------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

4.2.5 truncate语句

truncate与delete的区别：

语句类型	特点
delete	DELETE删除表内容时仅删除内容，但会保留表结构 DELETE语句每次删除一行，并在事务日志中为所删除的每行记录一项 可以通过回滚事务日志恢复数据 非常占用空间
truncate	删除表中所有数据，且无法恢复 表结构、约束和索引等保持不变，新添加的行计数值重置为初始值 执行速度比DELETE快，且使用的系统和事务日志资源少 通过释放存储表数据所用的数据页来删除数据，并且只在事务日志中记录页的释放 对于有外键约束引用的表，不能使用TRUNCATE TABLE删除数据 不能用于加入了索引视图的表

//语法：TRUNCATE table_name;

mysql> select * from liu;
+----+------+--------------+-----+
| id | name | phone_numble | age |
+----+------+--------------+-----+
|  1 | liu  | 34343434343  |  32 |
|  2 | zhen | 13329232222  |  43 |
|  3 | chao | 13086024562  |  60 |
+----+------+--------------+-----+
3 rows in set (0.00 sec)

mysql> truncate liu;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from liu;
Empty set (0.00 sec)

mysql> desc liu;
+--------------+-------------+------+-----+---------+-------+
| Field        | Type        | Null | Key | Default | Extra |
+--------------+-------------+------+-----+---------+-------+
| id           | int(11)     | NO   |     | NULL    |       |
| name         | varchar(50) | YES  |     | NULL    |       |
| phone_numble | varchar(11) | YES  |     | NULL    |       |
| age          | tinyint(4)  | NO   |     | NULL    |       |
+--------------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

4.3 DCL操作

4.3.1 创建授权grant

权限类型(priv_type)

权限类型	代表什么？
ALL	所有权限
SELECT	读取内容的权限
INSERT	插入内容的权限
UPDATE	更新内容的权限
DELETE	删除内容的权限

指定要操作的对象db_name.table_name

表示方式	意义
.	所有库的所有表
db_name	指定库的所有表
db_name.table_name	指定库的指定表

WITH GRANT OPTION：被授权的用户可将自己的权限副本转赠给其他用户，说白点就是将自己的权限完全复制给另一个用户。不建议使用。

GRANT priv_type,... ON [object_type] db_name.table_name TO ‘username'@'host' [IDENTIFIED BY 'password'] [WITH GRANT OPTION];

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| liuzhenchao        |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

//授权liuzhenchao用户在数据库本机上登录访问所有数据库
mysql> grant all on *.* to 'liuzhenchao'@'localhost' identified by '123456';
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> grant all on *.* to 'liuzhenchao'@'127.0.0.1' identified by '123456';
Query OK, 0 rows affected, 1 warning (0.00 sec)

//授权liuzhenchao用户在192.168.56.20上远程登录访问liuzhenchao数据库
mysql> grant all on liuzhenchao.* to 'liuzhenchao'@'192.168.56.20' identified by '123456';
Query OK, 0 rows affected, 1 warning (0.00 sec)

//授权liuzhenchao用户在所有位置上远程登录访问liuzhenchao数据库
mysql> grant all on *.* to 'liuzhenchao'@'%' identified by '123456';
Query OK, 0 rows affected, 1 warning (0.00 sec)

4.3.2 查看授权

//查看当前登录用户的授权信息
mysql> show grants;
+---------------------------------------------------------------------+
| Grants for root@localhost                                           |
+---------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' WITH GRANT OPTION |
| GRANT PROXY ON ''@'' TO 'root'@'localhost' WITH GRANT OPTION        |
+---------------------------------------------------------------------+
2 rows in set (0.00 sec)

//查看指定用户liuzhenchao的授权信息
mysql> show grants for liuzhenchao;
+--------------------------------------------------+
| Grants for liuzhenchao@%                         |
+--------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'liuzhenchao'@'%' |
+--------------------------------------------------+
1 row in set (0.00 sec)

mysql> show grants for 'liuzhenchao'@'localhost';
+----------------------------------------------------------+
| Grants for liuzhenchao@localhost                         |
+----------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'liuzhenchao'@'localhost' |
+----------------------------------------------------------+
1 row in set (0.00 sec)

mysql> show grants for 'liuzhenchao'@'127.0.0.1';
+----------------------------------------------------------+
| Grants for liuzhenchao@127.0.0.1                         |
+----------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'liuzhenchao'@'127.0.0.1' |
+----------------------------------------------------------+
1 row in set (0.00 sec)

4.3.3 取消授权REVOKE

//语法：REVOKE priv_type,... ON db_name.table_name FROM 'username'@'host';

mysql> revoke all on *.* from 'liuzhenchao'@'192.168.56.20';
Query OK, 0 rows affected (0.00 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

注意：mysql服务进程启动时会读取mysql库中的所有授权表至内存中：

• GRANT或REVOKE等执行权限操作会保存于表中，mysql的服务进程会自动重读授权表，并更新至内存中
• 对于不能够或不能及时重读授权表的命令，可手动让mysql的服务进程重读授权表 mysql> FLUSH PRIVILEGES;