Linux服务-mysql基础篇

mysql基础

目录

• 1. 关系型数据库介绍
  • 1.1 数据结构模型
  • 1.2 RDBMS专业名词
  • 1.3 关系型数据库的常见组件
  • 1.4 SQL语句
• 2. mysql安装与配置
  • 2.1 mysql安装
  • 2.2 mysql基本配置
• 3. mysql的程序组成
  • 3.1 mysql工具使用
  • 3.2 服务器监听的两种socket地址
• 4. mysql数据库操作
  • 4.1 DDL操作
    • 4.1.1 数据库操作
    • 4.1.2 表操作
    • 4.1.3 用户操作
    • 4.1.4 查看命令SHOW
    • 4.1.5 获取帮助
  • 4.2 DML操作（数据操控语言）
    • 4.2.1 INSERT语句
    • 4.2.2 SELECT语句
    • 4.2.3 update语句
    • 4.2.4 delete语句
    • 4.2.5 truncate语句
  • 4.3 DCL操作
    • 4.3.1 创建授权grant
    • 4.3.2 查看授权
    • 4.3.3 取消授权REVOKE

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

关系模型又分为:

• 二维关系：row(行)，column（列）
• 数据库管理系统：DBMS（database manager system）
• 关系数据库管理系统（Relational database manager system）

1.2 RDBMS专业名词

常见的关系型数据库管理系统：

• MySQL：MySQL，MariaDB（和MySQL是同源，RHEL7上yum源自带），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(整个事务中的所有操作，要么全部完成，要么全部不完成，不可能停滞在中间某个环节。事务在执行过程中发生错误，会被回滚（Rollback）到事务开始前的状态，就像这个事务从来没有执行过一样。)

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

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（一般是列）
• 连接（将两个表相关联）

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 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：
  
  1.rpm(有两种，os Vendor，项目官方提供)
  
  2.deb

//第一步下载mysql5.7的yum源
[root@cwh ~]# wget http://dev.mysql.com/get/mysql57-community-release-el7-10.noarch.rpm
--2019-04-22 15:04:39--  http://dev.mysql.com/get/mysql57-community-release-el7-10.noarch.rpm
...
...
2019-04-22 15:04:46 (389 KB/s) - 已保存 “mysql57-community-release-el7-10.noarch.rpm” [25548/25548])
[root@cwh ~]# ls
aaa  anaconda-ks.cfg  cwh4http.sh  httpd.conf  httpd-vhosts.conf  httppz1.sh  mysql57-community-release-el7-10.noarch.rpm

//第二步安装下载下来的mysql源
[root@cwh ~]# yum -y install mysql57-community-release-el7-10.noarch.rpm
[root@cwh ~]# ls /etc/yum.repos.d/
7CentOS-Base.repo  mysql-community.repo  mysql-community-source.repo  redhat.repo

//第三步安装mysql5.7
yum -y install mysql-community-server mysql-community-client mysql-community-common mysql-community-devel

2.2 mysql基本配置

//第一步启动mysql并查看端口是否开启
[root@cwh ~]# systemctl start mysqld
[root@cwh ~]# ss -antl
State       Recv-Q Send-Q                     Local Address:Port                                    Peer Address:Port
LISTEN      0      128                                    *:22                                                 *:*
LISTEN      0      100                            127.0.0.1:25                                                 *:*
LISTEN      0      80                                    :::3306                                              :::*
LISTEN      0      128                                   :::22                                                :::*
LISTEN      0      100                                  ::1:25                                                :::*                  

//第二步在mysql日志文件中找出mysql临时密码
[root@cwh ~]# cat /var/log/mysqld.log |grep password
2019-04-22T07:40:39.531315Z 1 [Note] A temporary password is generated for root@localhost: xB>aDF_l>4>;
//最后的xB>aDF_l>4>;为临时密码以后登陆时需要

//第三步使用获取到的临时密码登录mysql
[root@localhost ~]# mysql -uroot -p
Enter password:
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>   //这样显示出来了就表示临时登录成功

//第四步修改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 'cwh123!';
Query OK, 0 rows affected (0.00 sec)

mysql> quit
Bye

//第五步为避免mysql自动升级，这里需要卸载最开始安装的yum源
[root@localhost ~]# rpm -qa |grep mysql
mysql-community-common-5.7.25-1.el7.x86_64
mysql-community-libs-5.7.25-1.el7.x86_64
mysql-community-libs-compat-5.7.25-1.el7.x86_64
mysql-community-server-5.7.25-1.el7.x86_64
mysql57-community-release-el7-10.noarch
mysql-community-client-5.7.25-1.el7.x86_64
mysql-community-devel-5.7.25-1.el7.x86_64
[root@localhost ~]# yum -y remove mysql57-community-release-el7-10.noarch

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

//查看当前使用的mysql脚本
[root@localhost ~]# mysql -V
mysql  Ver 14.14 Distrib 5.7.25, for Linux (x86_64) using  EditLine wrapper

//本地登录
[root@cwh ~]# mysql -uroot -pcwh123! -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 13
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>  //此时显示已经登陆上了

//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@cwh ~]# mysql -uroot -p -h127.0.0.1
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 14
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> 

//查看mysql中有哪些数据库
[root@localhost ~]# 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chengweihong
[root@localhost ~]# mysql -uroot -p
Enter password:
mysql>
mysql> create database if not exists chengweihong;
Query OK, 1 row affected (0.00 sec)
mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| chengweihong       |
| 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chengweihong
mysql> drop database if exists chengweihong;
Query OK, 0 rows affected (0.02 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chengweihong里创建表cwh
//首先创建chengweihong数据库
mysql> create database chengweihong;
Query OK, 1 row affected (0.01 sec)
//在在数据库chengweihong中创建表
mysql> create table cwh(id int not null,name varchar(100),age tinyint);
Query OK, 0 rows affected (0.04 sec)
mysql> show tables;
+------------------------+
| Tables_in_chengweihong |
+------------------------+
| cwh                    |
+------------------------+
1 row in set (0.00 sec)
//具体查看表的内容
mysql> desc cwh;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id    | int(11)      | NO   |     | NULL    |       |
| name  | varchar(100) | YES  |     | NULL    |       |
| age   | tinyint(4)   | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
3 rows in set (0.03 sec)

//删除表
//语法：DROP TABLE [ IF EXISTS ] 'table_name';
//删除表cwh
mysql> drop table if exists cwh;
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wangqing
mysql> create user cwh@192.168.112.149 identified by 'cwh123!';
Query OK, 0 rows affected (0.01 sec)
//在192.168.112.149上验证
[root@149 ~]# mysql -ucwh -p -h192.168.112.146
Enter password:
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MySQL connection id is 19
Server version: 5.7.25 MySQL Community Server (GPL)

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

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

MySQL [(none)]>  //因为没有配置权限所以查看的东西有限，看不到chengweihong的数据库
MySQL [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
+--------------------+
1 row in set (0.01 sec)

//删除数据库用户
//语法：DROP USER 'username'@'host';
mysql> drop user cwh@192.168.112.149;
Query OK, 0 rows affected (0.01 sec)
//删除用户后在192.168.112.149主机上验证
[root@149 ~]# mysql -ucwh -p -h192.168.112.146
Enter password:
ERROR 1130 (HY000): Host '192.168.112.149' is not allowed to connect to this MySQL server
//可以看出已经无法登陆了

4.1.4 查看命令SHOW

//1.查看有哪些数据库
mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| chengweihong       |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

//2.查看数据库中有哪些表格（要看那个数据的表格就先进入到数据库中）
mysql> use chengweihong
Database changed
mysql> show tables;
+------------------------+
| Tables_in_chengweihong |
+------------------------+
| cwh                    |
+------------------------+
1 row in set (0.00 sec)

//3.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 |
| 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 |
| latin2   | ISO 8859-2 Central European     | latin2_general_ci   |      1 |
| swe7     | 7bit Swedish                    | swe7_swedish_ci     |      1 |
| ascii    | US ASCII                        | ascii_general_ci    |      1 |
| ujis     | EUC-JP Japanese                 | ujis_japanese_ci    |      3 |
| sjis     | Shift-JIS Japanese              | sjis_japanese_ci    |      2 |
| hebrew   | ISO 8859-8 Hebrew               | hebrew_general_ci   |      1 |
| tis620   | TIS620 Thai                     | tis620_thai_ci      |      1 |
| euckr    | EUC-KR Korean                   | euckr_korean_ci     |      2 |
| koi8u    | KOI8-U Ukrainian                | koi8u_general_ci    |      1 |
| gb2312   | GB2312 Simplified Chinese       | gb2312_chinese_ci   |      2 |
| greek    | ISO 8859-7 Greek                | greek_general_ci    |      1 |
| cp1250   | Windows Central European        | cp1250_general_ci   |      1 |
| gbk      | GBK Simplified Chinese          | gbk_chinese_ci      |      2 |
| latin5   | ISO 8859-9 Turkish              | latin5_turkish_ci   |      1 |
| armscii8 | ARMSCII-8 Armenian              | armscii8_general_ci |      1 |
| utf8     | UTF-8 Unicode                   | utf8_general_ci     |      3 |
| ucs2     | UCS-2 Unicode                   | ucs2_general_ci     |      2 |
| cp866    | DOS Russian                     | cp866_general_ci    |      1 |
| keybcs2  | DOS Kamenicky Czech-Slovak      | keybcs2_general_ci  |      1 |
| macce    | Mac Central European            | macce_general_ci    |      1 |
| macroman | Mac West European               | macroman_general_ci |      1 |
| cp852    | DOS Central European            | cp852_general_ci    |      1 |
| latin7   | ISO 8859-13 Baltic              | latin7_general_ci   |      1 |
| utf8mb4  | UTF-8 Unicode                   | utf8mb4_general_ci  |      4 |
| cp1251   | Windows Cyrillic                | cp1251_general_ci   |      1 |
| utf16    | UTF-16 Unicode                  | utf16_general_ci    |      4 |
| utf16le  | UTF-16LE Unicode                | utf16le_general_ci  |      4 |
| cp1256   | Windows Arabic                  | cp1256_general_ci   |      1 |
| cp1257   | Windows Baltic                  | cp1257_general_ci   |      1 |
| utf32    | UTF-32 Unicode                  | utf32_general_ci    |      4 |
| binary   | Binary pseudo charset           | binary              |      1 |
| geostd8  | GEOSTD8 Georgian                | geostd8_general_ci  |      1 |
| cp932    | SJIS for Windows Japanese       | cp932_japanese_ci   |      2 |
| eucjpms  | UJIS for Windows Japanese       | eucjpms_japanese_ci |      3 |
| gb18030  | China National Standard GB18030 | gb18030_chinese_ci  |      4 |
+----------+---------------------------------+---------------------+--------+
41 rows in set (0.01 sec)

//4.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)

//5.不进入某数据库而列出其包含的所有表
mysql> show tables from chengweihong;
+------------------------+
| Tables_in_chengweihong |
+------------------------+
| cwh                    |
+------------------------+
1 row in set (0.00 sec)

//6.查看表结构
//语法：DESC [db_name.]table_name;
mysql> desc chengweihong.cwh;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id    | int(11)      | NO   |     | NULL    |       |
| name  | varchar(100) | YES  |     | NULL    |       |
| age   | tinyint(4)   | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

//7.查看某表的创建命令
//语法：SHOW CREATE TABLE table_name;
mysql> show create table cwh;
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                             |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------+
| cwh   | CREATE TABLE `cwh` (
  `id` int(11) NOT NULL,
  `name` varchar(100) DEFAULT 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 create table cwh\G;
*************************** 1. row ***************************
       Table: cwh
Create Table: CREATE TABLE `cwh` (
  `id` int(11) NOT NULL,
  `name` varchar(100) DEFAULT NULL,
  `age` tinyint(4) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

4.1.5 获取帮助

//获取创建表的帮助
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]
    [partition_options]
    [IGNORE | REPLACE]
    [AS] query_expression

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    { LIKE old_tbl_name | (LIKE old_tbl_name) }

4.2 DML操作（数据操控语言）

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

1.一次插入一条完整数据

mysql> insert into cwh value(1,'tom',10);
Query OK, 1 row affected (0.01 sec)

mysql> select * from cwh;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | tom  |   10 |
+----+------+------+
1 row in set (0.00 sec)

2.一次插入多条完整数据

mysql> insert into cwh values(2,'jerry',20),(3,'natasha',30)
    -> ; //因为最后没有输入分号
Query OK, 2 rows affected (0.01 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from cwh
    -> ;  //因为ui后没输入；
+----+---------+------+
| id | name    | age  |
+----+---------+------+
|  1 | tom     |   10 |
|  2 | jerry   |   20 |
|  3 | natasha |   30 |
+----+---------+------+
3 rows in set (0.00 sec)

3.一次插入一条指定字段的数据

mysql> insert into cwh(id,name) value(4,'aaa');
Query OK, 1 row affected (0.00 sec)
mysql> select * from cwh;
+----+---------+------+
| id | name    | age  |
+----+---------+------+
|  1 | tom     |   10 |
|  2 | jerry   |   20 |
|  3 | natasha |   30 |
|  4 | aaa     | NULL |
+----+---------+------+
4 rows in set (0.00 sec)

4.一次插入多条指定字段的数据

mysql> insert into cwh(id,name) values(5,'bbb'),(6,'ccc');
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from cwh
    -> ;
+----+---------+------+
| id | name    | age  |
+----+---------+------+
|  1 | tom     |   10 |
|  2 | jerry   |   20 |
|  3 | natasha |   30 |
|  4 | aaa     | NULL |
|  5 | bbb     | NULL |
|  6 | ccc     | NULL |
+----+---------+------+
6 rows in set (0.00 sec)

4.2.2 SELECT语句

字段column表示法

表示符	表示
*	所有字段
as	字段别名, 当名字很长时用别名代替

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];

1.查看表的所有内容

mysql> select * from cwh;
+----+---------+------+
| id | name    | age  |
+----+---------+------+
|  1 | tom     |   10 |
|  2 | jerry   |   20 |
|  3 | natasha |   30 |
|  4 | aaa     | NULL |
|  5 | bbb     | NULL |
|  6 | ccc     | NULL |
+----+---------+------+
6 rows in set (0.00 sec)

2.按字段查看表的内容

mysql> select name from cwh;
+---------+
| name    |
+---------+
| tom     |
| jerry   |
| natasha |
| aaa     |
| bbb     |
| ccc     |
+---------+
6 rows in set (0.00 sec)

3.查看表的内容并按某字段升序排序

mysql> select * from cwh order by age;
+----+---------+------+
| id | name    | age  |
+----+---------+------+
|  4 | aaa     | NULL |
|  5 | bbb     | NULL |
|  6 | ccc     | NULL |
|  1 | tom     |   10 |
|  2 | jerry   |   20 |
|  3 | natasha |   30 |
+----+---------+------+
6 rows in set (0.00 sec)

4.查看表的内容按升序排序取前两个

mysql> select * from cwh order by id limit 2;
+----+-------+------+
| id | name  | age  |
+----+-------+------+
|  1 | tom   |   10 |
|  2 | jerry |   20 |
+----+-------+------+
2 rows in set (0.00 sec)

5.查看表的内容按升序排序跳过第一个取后两个

mysql> select * from cwh order by id limit 1,2;
+----+---------+------+
| id | name    | age  |
+----+---------+------+
|  2 | jerry   |   20 |
|  3 | natasha |   30 |
+----+---------+------+
2 rows in set (0.00 sec)

6.查看表的内容只打印age大于25的信息

mysql> select * from cwh where age >=25;
+----+---------+------+
| id | name    | age  |
+----+---------+------+
|  3 | natasha |   30 |
+----+---------+------+
1 row in set (0.00 sec)

7.查看表的内容只打印age=25和name=tom的信息

mysql> select * from cwh where age=10 and name='tom';
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | tom  |   10 |
+----+------+------+
1 row in set (0.00 sec)

8.查看表格打印id在2-4之间的信息

mysql> select * from cwh where id between 2 and 4;
+----+---------+------+
| id | name    | age  |
+----+---------+------+
|  2 | jerry   |   20 |
|  3 | natasha |   30 |
|  4 | aaa     | NULL |
+----+---------+------+
3 rows in set (0.00 sec)

9.查看表格打印age为空的信息

mysql> select * from cwh where age is null;
+----+------+------+
| id | name | age  |
+----+------+------+
|  4 | aaa  | NULL |
|  5 | bbb  | NULL |
|  6 | ccc  | NULL |
+----+------+------+
3 rows in set (0.00 sec)

10.查看表格打印age不为空的信息

mysql> select * from cwh where age is not null;
+----+---------+------+
| id | name    | age  |
+----+---------+------+
|  1 | tom     |   10 |
|  2 | jerry   |   20 |
|  3 | natasha |   30 |
+----+---------+------+
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];

注意：此语句只能一条一条的修改记录，可以修改一条记录中的多个字段

1.修改表中的aaa的age由null改为40

mysql> update cwh set age=40 where name='aaa';
Query OK, 1 row affected (0.00 sec)
mysql> select * from cwh;
+----+---------+------+
| id | name    | age  |
+----+---------+------+
|  1 | tom     |   10 |
|  2 | jerry   |   20 |
|  3 | natasha |   30 |
|  4 | aaa     |   40 |
|  5 | bbb     | NULL |
|  6 | ccc     | NULL |
+----+---------+------+
6 rows in set (0.00 sec)

2.修改表中一行记录中多个字段将id=6的ccc改为cwh，age改为60

mysql> update cwh set name='cwh',age=60 where id=6;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from cwh;
+----+---------+------+
| id | name    | age  |
+----+---------+------+
|  1 | tom     |   10 |
|  2 | jerry   |   20 |
|  3 | natasha |   30 |
|  4 | aaa     |   40 |
|  5 | bbb     | NULL |
|  6 | cwh     |   60 |
+----+---------+------+
6 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];

1.删除某条记录

mysql> select * from cwh;
+----+---------+------+
| id | name    | age  |
+----+---------+------+
|  1 | tom     |   10 |
|  2 | jerry   |   20 |
|  3 | natasha |   30 |
|  4 | aaa     |   40 |
|  5 | bbb     | NULL |
|  6 | cwh     |   60 |
+----+---------+------+
6 rows in set (0.00 sec)

mysql> delete from cwh where id=5;
Query OK, 1 row affected (0.00 sec)

mysql> select * from cwh;
+----+---------+------+
| id | name    | age  |
+----+---------+------+
|  1 | tom     |   10 |
|  2 | jerry   |   20 |
|  3 | natasha |   30 |
|  4 | aaa     |   40 |
|  6 | cwh     |   60 |
+----+---------+------+
5 rows in set (0.00 sec)

2.删除整个表的内容

mysql> select * from cwh111;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | qqq  |   10 |
|  2 | www  |   20 |
+----+------+------+
2 rows in set (0.00 sec)

mysql> delete from cwh111;
Query OK, 2 rows affected (0.00 sec)

mysql> select * from cwh111;
Empty 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

mysql> select * from cwh111;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | qqq  |   10 |
|  2 | www  |   20 |
+----+------+------+
2 rows in set (0.00 sec)

mysql> truncate cwh111;
Query OK, 0 rows affected (0.01 sec)
mysql> select * from cwh111;
Empty 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。

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

1.授权cwh用户在数据库本机上登录访问所有数据库

mysql> grant all on *.* to cwh@127.0.0.1 identified by '+7p6Mg2JsHgX1bIaOSwSykG8O2M='; //此处密码使用openssl rand 20 -base64 生成
mysql> show grants for cwh@127.0.0.1
    -> ;
+--------------------------------------------------+
| Grants for cwh@127.0.0.1                         |
+--------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'cwh'@'127.0.0.1' |
+--------------------------------------------------+
1 row in set (0.00 sec)

2.授权cwh用户在192.168.112.149上远程登录访问chengweihong数据库

//首先授权
mysql> grant all on chengweihong.* to cwh@192.168.112.149 identifiied by '+7p6Mg2JsHgX1bIaOSwSykG8O2M=';
Query OK, 0 rows affected, 1 warning (0.00 sec)
//在查看授权内容
mysql> show grants for cwh@192.168.112.149;
+---------------------------------------------------------------------+
| Grants for cwh@192.168.112.149                                      |
+---------------------------------------------------------------------+
| GRANT USAGE ON *.* TO 'cwh'@'192.168.112.149'                       |
| GRANT ALL PRIVILEGES ON `chengweihong`.* TO 'cwh'@'192.168.112.149' |
+---------------------------------------------------------------------+
2 rows in set (0.00 sec)
//最后在192.168.112.149主机上验证
[root@146 ~]# mysql -ucwh -p -h192.168.112.146
Enter password: 

MySQL [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| chengweihong       |
+--------------------+
2 rows in set (0.00 sec)

MySQL [chengweihong]> show tables;
+------------------------+
| Tables_in_chengweihong |
+------------------------+
| cwh                    |
| cwh111                 |
+------------------------+
2 rows in set (0.00 sec)

3.授权cwh用户在所有位置上远程登录访问chengweihong数据库的cwh表

//首先授权
mysql> grant all on chengweihong.cwh to 'cwh'@'%' identified by '+7p6Mg2JsHgX1bIaOSwSykG8O2M=';
Query OK, 0 rows affected, 1 warning (0.00 sec)
//在查看权限
mysql> show grants for cwh@'%';
+-----------------------------------------------------------+
| Grants for cwh@%                                          |
+-----------------------------------------------------------+
| GRANT USAGE ON *.* TO 'cwh'@'%'                           |
| GRANT ALL PRIVILEGES ON `chengweihong`.`cwh` TO 'cwh'@'%' |
+-----------------------------------------------------------+
2 rows in set (0.00 sec)
//在146主机上验证
[root@146 ~]# mysql -ucwh -p -h192.168.112.146
Enter password:
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MySQL connection id is 11
Server version: 5.7.25 MySQL Community Server (GPL)

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

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

MySQL [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| chengweihong       |
+--------------------+
2 rows in set (0.00 sec)

MySQL [(none)]> show tables from chengweihong;
+------------------------+
| Tables_in_chengweihong |
+------------------------+
| cwh                    |
+------------------------+
1 row in set (0.00 sec)

4.3.2 查看授权

1.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)

2.查看指定用户cwh的授权信息

mysql> show grants for cwh@'%';
+-----------------------------------------------------------+
| Grants for cwh@%                                          |
+-----------------------------------------------------------+
| GRANT USAGE ON *.* TO 'cwh'@'%'                           |
| GRANT ALL PRIVILEGES ON `chengweihong`.`cwh` TO 'cwh'@'%' |
+-----------------------------------------------------------+
2 rows 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';

1.取消对cwh用户的授权

mysql> revoke all on chengweihong.cwh from cwh@'%';
Query OK, 0 rows affected (0.00 sec)

mysql> show grants for cwh@'%';
+---------------------------------+
| Grants for cwh@%                |
+---------------------------------+
| GRANT USAGE ON *.* TO 'cwh'@'%' |
+---------------------------------+
1 row in set (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

刷新授权表：

mysql> FLUSH PRIVILEGES;