mysql基础

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文章标签： mysql 数据库

于 2022-07-25 21:10:14 首次发布

本文链接：https://blog.youkuaiyun.com/weixin_56774628/article/details/125983479

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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

**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

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 DELETE：删除表中数据 UPDATE：更新表中数据
SEL	ECT：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

[root@cl ~]# wget http://dev.mysql.com/get/mysql57-community-release-el7-11.noarch.rpm
[root@cl ~]# ls
anaconda-ks.cfg        httpd-2.4.51
apr-1.7.0              mysql57-community-release-el7-11.noarch.rpm
apr-util-1.6.1.tar.gz
//禁用mysql
[root@cl ~]# rpm -Uvh  mysql57-community-release-el7-11.noarch.rpm
[root@cl ~]# yum module disable mysql
[root@cl ~]# yum -y install mysql-community-server   --nogpgcheck
Last metadata expiration check: 0:02:08 ago on Mon 25 Jul 2022 05:17:45 PM CST.
Dependencies resolved.
==========================================================================
 Package                Arch   Version            Repository         Size
==========================================================================
Installing:
 mysql-community-server x86_64 5.7.38-1.el7       mysql57-community 178 M
Installing dependencies:
 mysql-community-client x86_64 5.7.38-1.el7       mysql57-community  28 M
 mysql-community-common x86_64 5.7.38-1.el7       mysql57-community 311 k
 mysql-community-libs   x86_64 5.7.38-1.el7       mysql57-community 2.6 M
 ncurses-compat-libs    x86_64 6.1-9.20180224.el8 base              328 k

Transaction Summary
==========================================================================
Install  5 Packages

Total download size: 208 M
Installed size: 891 M
Downloading Packages:
(1/5): ncurses-compat-libs-6.1-9.20180224 291 kB/s | 328 kB     00:01    
(2/5): mysql-community-common-5.7.38-1.el 271 kB/s | 311 kB     00:01    
(3/5): mysql-community-libs-5.7.38-1.el7. 300 kB/s | 2.6 MB     00:08    
(4/5): mysql-community-client-5.7.38-1.el 741 kB/s |  28 MB     00:38    
(5/5): mysql-community-server-5.7.38-1.el 3.1 MB/s | 178 MB     00:56    
--------------------------------------------------------------------------
Total                                     3.6 MB/s | 208 MB     00:58     
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
  Preparing        :                                                  1/1 
  Installing       : mysql-community-common-5.7.38-1.el7.x86_64       1/5 
  Installing       : mysql-community-libs-5.7.38-1.el7.x86_64         2/5 
  Running scriptlet: mysql-community-libs-5.7.38-1.el7.x86_64         2/5 
  Installing       : ncurses-compat-libs-6.1-9.20180224.el8.x86_64    3/5 
  Installing       : mysql-community-client-5.7.38-1.el7.x86_64       4/5 
  Running scriptlet: mysql-community-server-5.7.38-1.el7.x86_64       5/5 
  Installing       : mysql-community-server-5.7.38-1.el7.x86_64       5/5 
  Running scriptlet: mysql-community-server-5.7.38-1.el7.x86_64       5/5 
[/usr/lib/tmpfiles.d/mysql.conf:23] Line references path below legacy directory /var/run/, updating /var/run/mysqld → /run/mysqld; please update the tmpfiles.d/ drop-in file accordingly.

  Verifying        : ncurses-compat-libs-6.1-9.20180224.el8.x86_64    1/5 
  Verifying        : mysql-community-client-5.7.38-1.el7.x86_64       2/5 
  Verifying        : mysql-community-common-5.7.38-1.el7.x86_64       3/5 
  Verifying        : mysql-community-libs-5.7.38-1.el7.x86_64         4/5 
  Verifying        : mysql-community-server-5.7.38-1.el7.x86_64       5/5 

Installed:
  mysql-community-client-5.7.38-1.el7.x86_64                              
  mysql-community-common-5.7.38-1.el7.x86_64                              
  mysql-community-libs-5.7.38-1.el7.x86_64                                
  mysql-community-server-5.7.38-1.el7.x86_64                              
  ncurses-compat-libs-6.1-9.20180224.el8.x86_64                           

Complete!

2.2 mysql配置

//启动mysql并设置开机自动启动
[root@cl ~]# systemctl enable --now mysqld
[root@cl ~]# systemctl status mysqld
● mysqld.service - MySQL Server
   Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendo>
   Active: active (running) since Mon 2022-07-25 17:25:34 CST; 6s ago
     Docs: man:mysqld(8)
           http://dev.mysql.com/doc/refman/en/using-systemd.html
  Process: 3253 ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/var/ru>
  Process: 3203 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, st>
 Main PID: 3255 (mysqld)
    Tasks: 27 (limit: 12254)
   Memory: 300.9M
   CGroup: /system.slice/mysqld.service
           └─3255 /usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld>

Jul 25 17:25:32 cl systemd[1]: Starting MySQL Server...
Jul 25 17:25:34 cl systemd[1]: Started MySQL Server.
//确保3306端口已经监听起来
[root@cl ~]# ss -antl
State   Recv-Q  Send-Q   Local Address:Port   Peer Address:Port  Process  
LISTEN  0       128            0.0.0.0:22          0.0.0.0:*              
LISTEN  0       128               [::]:22             [::]:*              
LISTEN  0       128                  *:443               *:*              
LISTEN  0       80                   *:3306              *:*              
LISTEN  0       128                  *:80                *:* 
//在日志文件中找出临时密码
[root@cl ~]# grep "password" /var/log/mysqld.log 
2022-07-25T09:25:32.610802Z 1 [Note] A temporary password is generated for root@localhost: 8&#dfenhS6h!
//使用获取到的临时密码登录mysql并修改密码
[root@cl ~]# mysql -uroot -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.7.38

Copyright (c) 2000, 2022, Oracle and/or its affiliates.

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> 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 'chenlang123!';
Query OK, 0 rows affected (0.00 sec)

mysql> exit
Bye
//为避免mysql自动升级，这里需要卸载最开始安装的yum源
rpm -e mysql57-community-release

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@cl ~]# mysql -V
mysql  Ver 14.14 Distrib 5.7.38, for Linux (x86_64) using  EditLine wrapper
[root@cl ~]# mysql -uroot -pchenlang123! -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 6
Server version: 5.7.38 MySQL Community Server (GPL)

Copyright (c) 2000, 2022, Oracle and/or its affiliates.

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@cl ~]# mysql -uroot -p 
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 7
Server version: 5.7.38 MySQL Community Server (GPL)

Copyright (c) 2000, 2022, Oracle and/or its affiliates.

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@cl ~]# mysql -uroot -p -h 127.0.0.1 -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chenlang
mysql> create database chenlang;
Query OK, 1 row affected (0.00 sec)

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| chenlang           |
| 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chenlang
mysql> drop database chenlang;
Query OK, 0 rows affected (0.01 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chenlang里创建表cl
mysql> create database chenlang;
Query OK, 1 row affected (0.00 sec)

mysql> use chenlang;
Database changed
mysql> create table cl (id int not null,name varchar(10) not null,age tinyint);
Query OK, 0 rows affected (0.01 sec)
//查看当前数据库有哪些表
mysql> show tables;
+--------------------+
| Tables_in_chenlang |
+--------------------+
| cl                 |
+--------------------+
1 row in set (0.00 sec)
//删除表
//语法：DROP TABLE [ IF EXISTS ] 'table_name';
//删除表cl
mysql> drop table cl;
Query OK, 0 rows affected (0.00 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cl
mysql> create user 'cl'@'127.0.0.1' identified by 'chenlang123!';
Query OK, 0 rows affected (0.00 sec)
//使用新创建的用户和密码登录
[root@cl ~]# mysql -ucl -pchenlang123! -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: 5.7.38 MySQL Community Server (GPL)

Copyright (c) 2000, 2022, Oracle and/or its affiliates.

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 'cl'@'127.0.0.1';
Query OK, 0 rows affected (0.00 sec)

4.1.4 查看命令SHOW

//查看支持的所有字符集
mysql> show character set;
+----------+---------------------------------+---------------------+--------+
| 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 |
...
//查看当前数据库支持的所有存储引擎
mysql> show engines;
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| 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)
//查看数据库信息
mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| chenlang           |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)
//不进入某数据库而列出其包含的所有表
mysql> show tables from chenlang;
+--------------------+
| Tables_in_chenlang |
+--------------------+
| cl                 |
+--------------------+
1 row in set (0.00 sec)
//查看表结构
//语法：DESC [db_name.]table_name;
mysql> desc chenlang.cl;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | NO   |     | NULL    |       |
| name  | varchar(10) | NO   |     | NULL    |       |
| age   | tinyint(4)  | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.01 sec)
//查看某表的创建命令
//语法：SHOW CREATE TABLE table_name;
mysql> show create table chenlang.cl;
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                       |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------+
| cl    | CREATE TABLE `cl` (
  `id` int(11) NOT NULL,
  `name` varchar(10) NOT NULL,
  `age` tinyint(4) 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> show table status like 'cl' \G
*************************** 1. row ***************************
           Name: cl
         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: 2022-07-25 19:16:36
    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;
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]
...
...

MySQL 数据类型
&nbsp&nbsp&nbsp&nbsp&nbspMySQL中定义数据字段的类型对数据库的优化是非常重要的。MySQL支持多种类型，大致可以分为三类：数值、日期/时间和字符串(字符)类型。

数值类型
&nbsp&nbsp&nbsp&nbsp&nbspMySQL支持所有标准SQL数值数据类型。这些类型包括严格数值数据类型(INTEGER、SMALLINT、DECIMAL和NUMERIC)，以及近似数值数据类型(FLOAT、REAL和DOUBLE PRECISION)。
&nbsp&nbsp&nbsp&nbsp关键字INT是INTEGER的同义词，关键字DEC是DECIMAL的同义词。BIT数据类型保存位字段值，并且支持MyISAM、MEMORY、InnoDB和BDB表。作为SQL标准的扩展，MySQL也支持整数类型TINYINT、MEDIUMINT和BIGINT。下面的表显示了需要的每个整数类型的存储和范围
在这里插入图片描述

日期和时间类型
&nbsp&nbsp&nbsp&nbsp表示时间值的日期和时间类型为DATETIME、DATE、TIMESTAMP、TIME和YEAR。每个时间类型有一个有效值范围和一个"零"值，当指定不合法的MySQL不能表示的值时使用"零"值。TIMESTAMP类型有专有的自动更新特性，将在后面描述。
在这里插入图片描述

字符串类型
&nbsp&nbsp&nbsp&nbsp字符串类型指CHAR、VARCHAR、BINARY、VARBINARY、BLOB、TEXT、ENUM和SET。该节描述了这些类型如何工作以及如何在查询中使用这些类型。
在这里插入图片描述

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 chenlang;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> insert into cl (id,name,age) values (1,'cc',18),(2,'ll',19),(3,'aa',20);
Query OK, 3 rows affected (0.01 sec)
Records: 3  Duplicates: 0  Warnings: 0

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> select * from cl;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | cc   |   18 |
|  2 | ll   |   19 |
|  3 | aa   |   20 |
+----+------+------+
3 rows in set (0.01 sec)
//查找姓名这一列
mysql> select name from cl;
+------+
| name |
+------+
| cc   |
| ll   |
| aa   |
+------+
3 rows in set (0.00 sec)
//以年龄大小排序
mysql> select * from cl order by age;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | cc   |   18 |
|  2 | ll   |   19 |
|  3 | aa   |   20 |
+----+------+------+
3 rows in set (0.00 sec)
//以年龄大小逆向排序
mysql> select * from cl order by age desc;
+----+------+------+
| id | name | age  |
+----+------+------+
|  3 | aa   |   20 |
|  2 | ll   |   19 |
|  1 | cc   |   18 |
+----+------+------+
3 rows in set (0.00 sec)
//在排序时跳过第一个结果
mysql> select * from cl order by age limit 1,2;
+----+------+------+
| id | name | age  |
+----+------+------+
|  2 | ll   |   19 |
|  3 | aa   |   20 |
+----+------+------+
2 rows in set (0.00 sec)
//查找年龄大于等于19岁的结果
mysql> select * from cl where age >= 19;
+----+------+------+
| id | name | age  |
+----+------+------+
|  2 | ll   |   19 |
|  3 | aa   |   20 |
+----+------+------+
2 rows in set (0.01 sec)
//同时满足大于19岁和名字叫ll
mysql> select * from cl where age >= 19 and name = 'll';
+----+------+------+
| id | name | age  |
+----+------+------+
|  2 | ll   |   19 |
+----+------+------+
1 row in set (0.00 sec)
//查找年龄在18到20岁之间的结果
mysql> select * from cl where age between 18 and 20;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | cc   |   18 |
|  2 | ll   |   19 |
|  3 | aa   |   20 |
+----+------+------+
3 rows in set (0.00 sec)
//查找年龄不是空值的结果
mysql> select * from cl where age is not null;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | cc   |   18 |
|  2 | ll   |   19 |
|  3 | aa   |   20 |
+----+------+------+
3 rows 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 cl;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | cc   |   18 |
|  2 | ll   |   19 |
|  3 | aa   |   20 |
+----+------+------+
3 rows in set (0.00 sec)

mysql> update cl set age = 22 where id = 1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select *from cl;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | cc   |   22 |
|  2 | ll   |   19 |
|  3 | aa   |   20 |
+----+------+------+
3 rows 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> delete from cl where id = 2;
Query OK, 1 row affected (0.00 sec)

mysql> select *from cl;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | cc   |   22 |
|  3 | aa   |   20 |
+----+------+------+
2 rows in set (0.00 sec)
mysql> delete from cl;
Query OK, 2 rows affected (0.00 sec)

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

mysql> desc cl;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | NO   |     | NULL    |       |
| name  | varchar(10) | NO   |     | NULL    |       |
| age   | tinyint(4)  | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 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

mysql> select * from chenlang;
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  1 | tom      |   22 |
|  2 | zhangsan |   23 |
|  3 | lisi     |   24 |
|  4 | wangwu   |   26 |
|  5 | tom      |   30 |
|  6 | cl       |   20 |
|  7 | haha     | NULL |
+----+----------+------+
7 rows in set (0.00 sec)

mysql> truncate chenlang;
Query OK, 0 rows affected (0.01 sec)

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

mysql> desc chenlang;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id    | int(11)      | NO   |     | NULL    |       |
| name  | varchar(100) | NO   |     | NULL    |       |
| age   | tinyint(4)   | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
3 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 |
| mysql              |
| performance_schema |
| sys                |
| chenlang         |
+--------------------+
5 rows in set (0.00 sec)

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

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

//授权wangqing用户在192.168.58.130上远程登录访问chenlang数据库
mysql> grant all on chenlang.* to 'cl'@'192.168.58.130' identified by '123456';
Query OK, 0 rows affected, 1 warning (0.00 sec)

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

4.3.1.1 使用Navicat Premium 进行连接测试

//授权root用户在192.168.58.130上远程登录访问所有数据库的权限
//授权root用户在本物理机192.168.58.1网段上远程登录访问所有数据库的权限
mysql> grant all on *.* to 'root'@'192.168.58.130' identified by '1234566';
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> grant all on *.* to 'root'@'192.168.58.1'  identified by '123456';
Query OK, 0 rows affected, 1 warning (0.00 sec)

在这里插入图片描述

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wangqing的授权信息
mysql> show grants for cl;
+------------------------------------------+
| Grants for cl@%                         |
+------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'cl'@'%' |
+------------------------------------------+
1 row in set (0.00 sec)

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

mysql> show grants for 'cl'@'127.0.0.1';
+--------------------------------------------------+
| Grants for cl@127.0.0.1                         |
+--------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'cl'@'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 'cl'@'192.168.58.130';
Query OK, 0 rows affected (0.00 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.01 sec)