mysql

1.SQL概述

1.1SQL语言特点

1.是一种一体化语言 
集数据定义、数据操纵、数据控制功能于一体。可以完成数据库中全部操作，包括定义关系模式、录入数据、查询、维护等。
2.是一种高度非过程化语言 
不需一步步告诉“如何做”，只需描述“做什么”。SQL可将要求交与系统自动完成。存取路径的选择以及SQL语句的操作过程由系统自动完成。减轻了用户负担，而且有利于提高数据独立性。
3.语言非常简洁
只用9动词就能完成数据核心功能。数据定义：create,drop,alter,数据操纵：SELECT INSERT、UPDATE、DELETE；数据控制： GRANT （设置用户权限）、REVOKE（取消设置用户权限）。
4.同一种语法结构提供两种使用方式

• 自含式语言：能够独立地用于联机交互的使用方式。
• 嵌入式语言：即将SQL嵌入到其他高级语言中使用。

2. 关系型数据库介绍

2.1 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

2.2 RDBMS

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

MySQL数据库管理系统数据表字段约束主要包括主键约束、外键约束、默认值约束、唯一约束、空值约束、自动增长约束等。

1.主键约束 Primary Key
主键的概念：记录的唯一标识，能够通过该标识确定唯一一条记录。如上表中唯一能够确定学生记录的只能是学号，因此学号是主键。主键是不允许为空，不允许出现重复。可以在定义数据表字段时给字段添加主键约束。语法结构为 ：
//字段名称 数据类型 主键约束
id varchar(14) primary key
如上表所示，定义学生学号字段名称为id ，数据类型为可变长度字符串，长度为14 ，设置其为主键。
在定义主键时需要注意多字段组合形式主键的定义，在很多情况下我们的主键需要由多个字段所组成，如学生成绩信息表，主要字段包括学号、课程编号、成绩。针对该表主键为学号与课程编号组合。
primary key(id,cid)
//id指学号
//cid指课程编号
2、外键约束 Foreign Key
外键约束主要针对多个表之间的关系进行描述，外键的定义描述如下：
对于字段F在表A中不是主键，但在另外一个表B中表示主键，这个时候字段F对于表A可称为外键，在定义过程中需指明F在哪个表中是主键。另外需要注意，两个表中并不需要都是用F作为字段名，只要两者存储数据含义与类型一致即可。为说明外键约束，我们使用学生基本信息表与班级信息表进行说明，表结构存储数据描述如下图：

如上表所示，学生信息表与班级信息表中均存在一个班级编号字段，在学生信息表中，该字段不表示任何键，但在班级信息表中编辑编码为主键，因此相对于学生信息表，班级编号为外键。实现语法描述如下：
constraint stu_class_fk foreign key (class_id) references classinfor(class_id)
//由于存在外键关系需要首先定义班级信息表classinfor,再定义学生信息表
// 在定义学生信息表stuinfor中定义外键约束
//stu_class_fk表示外键名称
//references表示外键依赖关系
3、默认值约束 default
默认值约束主要用于实现为字段提供统一的默认值，如学生信息表中，所有的班级编号字段都取值1，为简化操作，我们可以直接为班级编号定义默认值约束，取值为1，在后期录入数据时，可直接去掉对该字段的数据录入。在定义字段时可直接指明默认值，基本语法：
字段名称 数据类型 默认值
class_id varchar(4) default “1”;
//设置学生信息表中学号字段默认值为1
4.唯一约束unique
唯一约束主要用于约束字段取值的唯一性，有些情况下需要在录入数据时保存数据的唯一性，如在上表学生信息表中，需要学生的联系电话唯一，即该字段不允许输入重复的值。示例代码如下：
字段名称 数据类型 unique
stu_tel varchar(14) unique
//设置学生电话字段名称为stu_tel
//类型为长度14字符串
//唯一约束
5.空值约束 NULL
字段允许取空值则可使用空值约束，默认情况下，字段是允许为空的。如我们创建一个学生成绩表，在录入成绩之前需要将学号，课程编号写入数据表，但是允许成绩为空时，对成绩字段设置允许为空。代码说明如下：
字段名称 数据类型 null | not null
stu_score float(4) null
//设置学生成绩字段名称为stu_score
//类型为浮点型
//设置允许为空
6.自动增长约束 auto_increment
自动增长可以理解为一种约束，也可以理解为一种数据类型。是指某一个字段值依次增长，且不重复，（序号）在这种情况下可以将其设置为自动增长类型。如我们可以将班级信息表中的班级编号设置为自动增长字段：
class_id int auto_increment primary key;
//班级编号 class_id
//数据类型 int整数
//自动增长，默认初始值1，增量1
//主键 primary key

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

2.3 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

2.4 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

3. mysql安装与配置

3.1 mysql安装

[root@yanlei ~]# yum -y install mariadb*
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: mirrors.aliyun.com
 * extras: mirrors.aliyun.com
 * updates: mirrors.aliyun.com
base                       | 3.6 kB     00:00     
extras                     | 2.9 kB     00:00     
updates                    | 2.9 kB     00:00     
Package 1:mariadb-embedded-5.5.65-1.el7.x86_64 already installed and latest version
Package 1:mariadb-server-5.5.65-1.el7.x86_64 already installed and latest version
Package 1:mariadb-test-5.5.65-1.el7.x86_64 already installed and latest version
Package 1:mariadb-devel-5.5.65-1.el7.x86_64 already installed and latest version
Package 1:mariadb-bench-5.5.65-1.el7.x86_64 already installed and latest version
Package 1:mariadb-embedded-devel-5.5.65-1.el7.x86_64 already installed and latest version
Package 1:mariadb-5.5.65-1.el7.x86_64 already installed and latest version
Package 1:mariadb-libs-5.5.65-1.el7.x86_64 already installed and latest version
Nothing to do

3.2mysql配置

1.启动mysql

[root@yanlei ~]# systemctl enable --now mariadb
Created symlink from /etc/systemd/system/multi-user.target.wants/mariadb.service to /usr/lib/systemd/system/mariadb.service.
[root@yanlei ~]# systemctl status mariadb
● mariadb.service - MariaDB database server
   Loaded: loaded (/usr/lib/systemd/system/mariadb.service; enabled; vendor preset: disabled)
   Active: active (running) since Wed 2020-05-20 14:08:53 CST; 2s ago
  Process: 2762 ExecStartPost=/usr/libexec/mariadb-wait-ready $MAINPID (code=exited, status=0/SUCCESS)

2.查看监听端口3306

[root@yanlei ~]# ss -tanl
State      Recv-Q Send-Q Local Address:Port               Peer Address:Port              
LISTEN     0      50      *:3306                *:*                  
LISTEN     0      128     *:22                  *:*                  
LISTEN     0      100    127.0.0.1:25                  *:*                  
LISTEN     0      128    :::22                 :::*                  
LISTEN     0      100       ::1:25                 :::*                  

3.设置登录mysql密码

[root@yanlei ~]# mysql
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 2
Server version: 5.5.65-MariaDB MariaDB Server

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

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

MariaDB [(none)]> set password = password('147258');

4. 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

4.1 mysql工具使用

语法：mysql [OPTIONS] [database]
常用的OPTIONS：

• -u //指定用户名，默认为root
• -h //指定服务器主机，默认为localhost，推荐使用ip地址
• -p //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

[root@yanlei ~]# mysql -uroot -p147258 -h127.0.0.1Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 6
Server version: 5.5.65-MariaDB MariaDB Server

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

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

MariaDB [(none)]> 

• -V //查看当前使用的mysql版本

[root@yanlei ~]# mysql -V
mysql  Ver 15.1 Distrib 5.5.65-MariaDB, for Linux (x86_64) using readline 5.1

• -e //不登录mysql执行sql语句后退出，常用于脚本

[root@yanlei ~]# mysql -uroot -p147258 -h127.0.0.1 -e 'show databases;'
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| test               |
+--------------------+

4.2 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

5. mysql数据库操作

5.1 DDL操作

5.1.1 数据库操作

//创建数据库
//语法：CREATE DATABASE [IF NOT EXISTS] 'DB_NAME';
//创建数据库hello
MariaDB [(none)]> create database if not exists hello;
Query OK, 1 row affected (0.00 sec)

MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| hello              |
| mysql              |
| performance_schema |
| test               |
+--------------------+
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hello
MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| hello              |
| mysql              |
| performance_schema |
| test               |
+--------------------+
5 rows in set (0.00 sec)

MariaDB [(none)]> drop database if exists hello;
Query OK, 0 rows affected (0.00 sec)

MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| test               |
+--------------------+
4 rows in set (0.00 sec)

5.1.2 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hello里创建表class
MariaDB [hello]> create table class (id int not null,name varchar(60) not null,age tinyint not null);
Query OK, 0 rows affected (0.00 sec)

MariaDB [hello]> show tables;
+-----------------+
| Tables_in_hello |
+-----------------+
| class           |
+-----------------+
1 row in set (0.00 sec)

MariaDB [hello]> desc class;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | NO   |     | NULL    |       |
| name  | varchar(60) | NO   |     | NULL    |       |
| age   | tinyint(4)  | NO   |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
MariaDB [hello]> select * from class;
Empty set (0.00 sec)

//删除表
//语法：DROP TABLE [ IF EXISTS ] 'table_name';
//删除表class
MariaDB [hello]> show tables;
+-----------------+
| Tables_in_hello |
+-----------------+
| class           |
+-----------------+
1 row in set (0.00 sec)

MariaDB [hello]> drop table class;
Query OK, 0 rows affected (0.01 sec)

MariaDB [hello]> show tables;
Empty set (0.00 sec)

MariaDB [hello]> 

5.1.3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lei
MariaDB [(none)]> create user 'lei'@'192.168.220.135' identified by '147258';
Query OK, 0 rows affected (0.00 sec)
//删除数据库用户
//语法：DROP USER 'username'@'host'; 
MariaDB [(none)]> drop user [email protected];
Query OK, 0 rows affected (0.00 sec)

MariaDB [(none)]> 

5.1.4 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 |
| 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 |
| 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 |


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 | Percona-XtraDB, Supports transactions, row-level locking, and foreign keys       | YES          | YES  | YES        |
| MRG_MYISAM         | YES     | Collection of identical MyISAM tables                                            | NO           | NO   | NO         |
| MyISAM             | YES     | Non-transactional engine with good performance and small data footprint          | NO           | NO   | NO         |
| BLACKHOLE          | YES     | /dev/null storage engine (anything you write to it disappears)                   | NO           | NO   | NO         |
| PERFORMANCE_SCHEMA | YES     | Performance Schema                                                               | NO           | NO   | NO         |
| CSV                | YES     | Stores tables as CSV files                                                       | NO           | NO   | NO         |
| ARCHIVE            | YES     | gzip-compresses tables for a low storage footprint                               | NO           | NO   | NO         |
| MEMORY             | YES     | Hash based, stored in memory, useful for temporary tables                        | NO           | NO   | NO         |
| FEDERATED          | YES     | Allows to access tables on other MariaDB servers, supports transactions and more | YES          | NO   | YES        |
| Aria               | YES     | Crash-safe tables with MyISAM heritage                                           | NO           | NO   | NO         |
+--------------------+---------+----------------------------------------------------------------------------------+--------------+------+------------+
10 rows in set (0.00 sec)


MariaDB [(none)]> SHOW ENGINES\G
*************************** 1. row ***************************
      Engine: InnoDB
     Support: DEFAULT
     Comment: Percona-XtraDB, Supports transactions, row-level locking, and foreign keys
Transactions: YES
          XA: YES
  Savepoints: YES
*************************** 2. row ***************************
      Engine: MRG_MYISAM
     Support: YES
     Comment: Collection of identical MyISAM tables
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 3. row ***************************
      Engine: MyISAM
     Support: YES
     Comment: Non-transactional engine with good performance and small data footprint
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 4. row ***************************
      Engine: BLACKHOLE
     Support: YES
     Comment: /dev/null storage engine (anything you write to it disappears)
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 5. row ***************************
      Engine: PERFORMANCE_SCHEMA
     Support: YES
     Comment: Performance Schema
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 6. row ***************************
      Engine: CSV
     Support: YES
     Comment: Stores tables as CSV files
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 7. row ***************************
      Engine: ARCHIVE
     Support: YES
     Comment: gzip-compresses tables for a low storage footprint
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 8. row ***************************
      Engine: MEMORY
     Support: YES
     Comment: Hash based, stored in memory, useful for temporary tables
Transactions: NO
          XA: NO
  Savepoints: NO
*************************** 9. row ***************************
      Engine: FEDERATED
     Support: YES
     Comment: Allows to access tables on other MariaDB servers, supports transactions and more
Transactions: YES
          XA: NO
  Savepoints: YES
*************************** 10. row ***************************
      Engine: Aria
     Support: YES
     Comment: Crash-safe tables with MyISAM heritage
Transactions: NO
          XA: NO
  Savepoints: NO
10 rows in set (0.00 sec)

mysql> SHOW DATABASES;          //查看数据库信息
MariaDB [(none)]> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| hello              |
| mysql              |
| performance_schema |
| test               |
+--------------------+
5 rows in set (0.00 sec)


mysql> SHOW TABLES FROM wangqingge;         //不进入某数据库而列出其包含的所有表
MariaDB [(none)]> SHOW TABLES FROM hello;
+-----------------+
| Tables_in_hello |
+-----------------+
| class           |
+-----------------+
1 row in set (0.00 sec)


//查看表结构
//语法：DESC [db_name.]table_name;
MariaDB [(none)]> desc hello.class;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | NO   |     | NULL    |       |
| name  | varchar(50) | NO   |     | NULL    |       |
| age   | tinyint(4)  | NO   |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

//查看某表的创建命令
//语法：SHOW CREATE TABLE table_name;
MariaDB [(none)]> SHOW CREATE TABLE hello.class;
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                      |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------+
| class | CREATE TABLE `class` (
  `id` int(11) NOT NULL,
  `name` varchar(50) NOT NULL,
  `age` tinyint(4) NOT 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
MariaDB [(none)]> use hello;
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
MariaDB [hello]> show table status like 'class'\G
*************************** 1. row ***************************
           Name: class
         Engine: InnoDB
        Version: 10
     Row_format: Compact
           Rows: 0
 Avg_row_length: 0
    Data_length: 16384
Max_data_length: 0
   Index_length: 0
      Data_free: 10485760
 Auto_increment: NULL
    Create_time: 2020-05-23 01:17:10
    Update_time: NULL
     Check_time: NULL
      Collation: latin1_swedish_ci
       Checksum: NULL
 Create_options: 
        Comment: 
1 row in set (0.00 sec)

MariaDB [hello]> 

5.1.5 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
MariaDB [hello]> HELP CREATE TABLE;
Name: 'CREATE TABLE'
Description:
Syntax:
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    (create_definition,...)
    [table_options]
    [partition_options]

Or:

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    [(create_definition,...)]
    [table_options]
    [partition_options]
    select_statement

Or:

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

create_definition:
    col_name column_definition
  | [CONSTRAINT [symbol]] PRIMARY KEY [index_type] (index_col_name,...)
      [index_option] ...
  | {INDEX|KEY} [index_name] [index_type] (index_col_name,...)
      [index_option] ...
  | [CONSTRAINT [symbol]] UNIQUE [INDEX|KEY]
      [index_name] [index_type] (index_col_name,...)
      [index_option] ...
  | {FULLTEXT|SPATIAL} [INDEX|KEY] [index_name] (index_col_name,...)
      [index_option] ...
  | [CONSTRAINT [symbol]] FOREIGN KEY
      [index_name] (index_col_name,...) reference_definition
  | CHECK (expr)

column_definition:
    data_type [NOT NULL | NULL] [DEFAULT default_value]

5.2 DML操作

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

5.2.1 INSERT语句

//DML操作之增操作insert
//语法：INSERT [INTO] table_name [(column_name,...)] {VALUES | VALUE} (value1,...),(...),...
MariaDB [hello]> desc class;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | NO   |     | NULL    |       |
| name  | varchar(50) | NO   |     | NULL    |       |
| age   | tinyint(4)  | NO   |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

MariaDB [hello]> insert into class value(1,'tom',23);
Query OK, 1 row affected (0.00 sec)
MariaDB [hello]> select * from class;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | tom  |  23 |
+----+------+-----+
1 row in set (0.00 sec)

MariaDB [hello]> insert into class value(2,'jee',18),(3,'yyu',24);
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

MariaDB [hello]> select * from class;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | tom  |  23 |
|  2 | jee  |  18 |
|  3 | yyu  |  24 |
+----+------+-----+
3 rows in set (0.00 sec)


MariaDB [hello]> desc yanlei;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id    | int(11)      | YES  |     | NULL    |       |
| name  | varchar(200) | YES  |     | NULL    |       |
| age   | tinyint(4)   | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

MariaDB [hello]> insert into yanlei(name) value('xiaowang');
Query OK, 1 row affected (0.00 sec)

MariaDB [hello]> select * from yanlei;
+------+----------+------+
| id   | name     | age  |
+------+----------+------+
| NULL | xiaowang | NULL |
+------+----------+------+
1 row in set (0.00 sec)

//设置id字段自动增长
MariaDB [hello]> create table xiaoxiao(id int primary key auto_increment not null,name varchar(50),age tinyint);
Query OK, 0 rows affected (0.00 sec)

MariaDB [hello]> desc xiaoxiao;
+-------+-------------+------+-----+---------+----------------+
| Field | Type        | Null | Key | Default | Extra          |
+-------+-------------+------+-----+---------+----------------+
| id    | int(11)     | NO   | PRI | NULL    | auto_increment |
| name  | varchar(50) | YES  |     | NULL    |                |
| age   | tinyint(4)  | YES  |     | NULL    |                |
+-------+-------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
MariaDB [hello]> insert xiaoxiao value(1,'tom',21);
Query OK, 1 row affected (0.00 sec)

MariaDB [hello]> select * from xiaoxiao;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | tom  |   21 |
+----+------+------+
1 row in set (0.00 sec)

MariaDB [hello]> insert xiaoxiao value('tom',21);
ERROR 1136 (21S01): Column count doesn't match value count at row 1
MariaDB [hello]> insert xiaoxiao(name,age) value('tom',21);
Query OK, 1 row affected (0.00 sec)

MariaDB [hello]> select * from xiaoxiao;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | tom  |   21 |
|  2 | tom  |   21 |
+----+------+------+
2 rows in set (0.00 sec)

5.2.2 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];
MariaDB [hello]> select * from class;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | tom  |  23 |
|  2 | jee  |  18 |
|  3 | yyu  |  24 |
+----+------+-----+
3 rows in set (0.00 sec)

MariaDB [hello]> select id,age from class
    -> ;
+----+-----+
| id | age |
+----+-----+
|  1 |  23 |
|  2 |  18 |
|  3 |  24 |
+----+-----+
3 rows in set (0.00 sec)

\\设置别名
MariaDB [hello]> select id as 编号,age from class
    -> ；
    -> ;
+--------+-----+
| 编号   | age |
+--------+-----+
|      1 |  23 |
|      2 |  18 |
|      3 |  24 |
+--------+-----+
3 rows in set (0.00 sec)

MariaDB [hello]> select * from class where age=18;+----+------+-----+
| id | name | age |
+----+------+-----+
|  2 | jee  |  18 |
+----+------+-----+
1 row in set (0.00 sec)

MariaDB [hello]> select neme from class where age=18;
ERROR 1054 (42S22): Unknown column 'neme' in 'field list'
MariaDB [hello]> select name from class where age=18;
+------+
| name |
+------+
| jee  |
+------+
1 row in set (0.00 sec)

MariaDB [hello]> select * from class where age=18 or name='tom';
+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | tom  |  23 |
|  2 | jee  |  18 |
+----+------+-----+
2 rows in set (0.00 sec)

MariaDB [hello]> select * from class where age=18 and name='jee';
+----+------+-----+
| id | name | age |
+----+------+-----+
|  2 | jee  |  18 |
+----+------+-----+
1 row in set (0.00 sec)


MariaDB [hello]> select * from class where age between 20 and 23;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | tom  |  23 |
+----+------+-----+
1 row in set (0.00 sec)

MariaDB [hello]> 


MariaDB [hello]> select * from class where age >= 20 and age <= 24;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | tom  |  23 |
|  3 | yyu  |  24 |
+----+------+-----+
2 rows in set (0.00 sec)


MariaDB [hello]> select * from class where age like '2%';
+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | tom  |  23 |
|  3 | yyu  |  24 |
+----+------+-----+
2 rows in set (0.00 sec)

MariaDB [hello]> select * from class where name rlike '^t[a-z][a-z]';
+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | tom  |  23 |
+----+------+-----+
1 row in set (0.00 sec)


MariaDB [hello]> select * from xiaoxiao;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | tom  |   21 |
|  2 | tom  |   21 |
|  3 | lisi | NULL |
+----+------+------+
3 rows in set (0.00 sec)

MariaDB [hello]> select * from xiaoxiao where age is not null;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | tom  |   21 |
|  2 | tom  |   21 |
+----+------+------+
2 rows in set (0.00 sec)

MariaDB [hello]> select * from xiaoxiao where age is null;
+----+------+------+
| id | name | age  |
+----+------+------+
|  3 | lisi | NULL |
+----+------+------+
1 row in set (0.00 sec)


MariaDB [hello]> select * from class order by age;+----+------+-----+
| id | name | age |
+----+------+-----+
|  2 | jee  |  18 |
|  1 | tom  |  23 |
|  3 | yyu  |  24 |
+----+------+-----+
3 rows in set (0.00 sec)

MariaDB [hello]> select * from class order by age limit 1;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  2 | jee  |  18 |
+----+------+-----+
1 row in set (0.00 sec)

MariaDB [hello]> select name from class order by age limit 1;
+------+
| name |
+------+
| jee  |
+------+
1 row in set (0.00 sec)

MariaDB [hello]> select * from class order by age ;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  2 | jee  |  18 |
|  1 | tom  |  23 |
|  3 | yyu  |  24 |
+----+------+-----+
3 rows in set (0.00 sec)

MariaDB [hello]> select * from class order by age limit 1,1;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | tom  |  23 |
+----+------+-----+
1 row in set (0.00 sec)

MariaDB [hello]> select * from class order by age limit 1,2;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | tom  |  23 |
|  3 | yyu  |  24 |
+----+------+-----+
2 rows in set (0.00 sec)

MariaDB [hello]> select * from class order by age limit 2,1;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  3 | yyu  |  24 |
+----+------+-----+
1 row in set (0.00 sec)

MariaDB [hello]> select * from class order by age desc;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  3 | yyu  |  24 |
|  1 | tom  |  23 |
|  2 | jee  |  18 |
+----+------+-----+
3 rows in set (0.00 sec)

MariaDB [hello]> select * from class order by age desc limit 1;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  3 | yyu  |  24 |
+----+------+-----+
1 row in set (0.00 sec)

5.2.3 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];

MariaDB [hello]> select * from class;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | tom  |  23 |
|  2 | jee  |  18 |
|  3 | yyu  |  24 |
+----+------+-----+
3 rows in set (0.00 sec)

MariaDB [hello]> update class set age = 25 where id = 2;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [hello]> select * from class;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | tom  |  23 |
|  2 | jee  |  25 |
|  3 | yyu  |  24 |
+----+------+-----+
3 rows in set (0.00 sec)

5.2.4 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];
MariaDB [hello]> select * from class;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | tom  |  23 |
|  2 | jee  |  25 |
|  3 | yyu  |  24 |
+----+------+-----+
3 rows in set (0.00 sec)

MariaDB [hello]> delete from class where id = 3;   删除某条记录
Query OK, 1 row affected (0.00 sec)

MariaDB [hello]> select * from class;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | tom  |  23 |
|  2 | jee  |  25 |
+----+------+-----+
2 rows in set (0.00 sec)

MariaDB [hello]> delete from yanlei;    删除整张表内容
Query OK, 1 row affected (0.00 sec)

MariaDB [hello]> show tables;
+-----------------+
| Tables_in_hello |
+-----------------+
| class           |
| xiaoxiao        |
| yanlei          |
+-----------------+
3 rows in set (0.00 sec)

MariaDB [hello]> select * from yanlei;
Empty set (0.00 sec)

5.2.5 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;
MariaDB [hello]> select * from class;
+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | tom  |  23 |
|  2 | jee  |  25 |
+----+------+-----+
2 rows in set (0.00 sec)

MariaDB [hello]> truncate class;
Query OK, 0 rows affected (0.00 sec)

MariaDB [hello]> select * from class;
Empty set (0.00 sec)

MariaDB [hello]> desc class;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | NO   |     | NULL    |       |
| name  | varchar(50) | NO   |     | NULL    |       |
| age   | tinyint(4)  | NO   |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

5.3 DCL操作

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];
MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| hello              |
| mysql              |
| performance_schema |
| test               |
+--------------------+
5 rows in set (0.00 sec)
//授权tom用户本机上hello库xiaoxiao表插入数据
MariaDB [(none)]> create user 'tom'@'localhost' identified by '147258';
Query OK, 0 rows affected (0.00 sec)

MariaDB [(none)]> grant insert on hello.xiaoxiao to 'tom'@'localhost';
Query OK, 0 rows affected (0.00 sec)
MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| hello              |
| test               |
+--------------------+
3 rows in set (0.00 sec)

MariaDB [(none)]> use hello;
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
MariaDB [hello]> show tables;
+-----------------+
| Tables_in_hello |
+-----------------+
| xiaoxiao        |
+-----------------+
1 row in set (0.00 sec)

MariaDB [hello]> select * from xiaoxiao;
ERROR 1142 (42000): SELECT command denied to user 'tom'@'localhost' for table 'xiaoxiao'
MariaDB [hello]> insert xiaoxiao(name,age) value('xiaozhang',15);
Query OK, 1 row affected (0.11 sec)

5.3.2 查看授权

当前用户权限
MariaDB [(none)]> show grants;
+----------------------------------------------------------------------------------------------------------------------------------------+
| Grants for root@localhost                                                                                                              |
+----------------------------------------------------------------------------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' IDENTIFIED BY PASSWORD '*288A7937D7A48B2C8148F1849013DBD8AA443263' WITH GRANT OPTION |
| GRANT PROXY ON ''@'' TO 'root'@'localhost' WITH GRANT OPTION                                                                           |
+----------------------------------------------------------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)
查看tom@localhost权限


MariaDB [(none)]> show grants for 'tom'@'localhost';
+------------------------------------------------------------------------------------------------------------+
| Grants for tom@localhost                                                                                   |
+------------------------------------------------------------------------------------------------------------+
| GRANT USAGE ON *.* TO 'tom'@'localhost' IDENTIFIED BY PASSWORD '*288A7937D7A48B2C8148F1849013DBD8AA443263' |
| GRANT INSERT ON `hello`.`xiaoxiao` TO 'tom'@'localhost'                                                    |
+------------------------------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)

5.3.3 取消授权REVOKE

//语法：REVOKE priv_type,... ON db_name.table_name FROM 'username'@'host';
MariaDB [(none)]> revoke select on *.* from 'tom'@'localhost';
Query OK, 0 rows affected (0.00 sec)

MariaDB [(none)]> flush privileges;    刷新权限
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

MariaDB [(none)]> flush privileges;    

破解mysql登录密码

1、打开mysql配置文件/etc/my.cnf在【mysqld】下面添加一行代码：skip-grant-tables。这行代码意思就是跳过跳过授权表，即是可以跳过密码验证直接进入数据库。

[root@yanlei ~]# vim /etc/my.cnf

[mysqld]
skip-grant-tables
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0
# Settings user and group are ignored when systemd is used.
# If you need to run mysqld under a different user or group,
# customize your systemd unit file for mariadb according to the

2.重启mysql数据库

[root@yanlei ~]# systemctl restart mariadb

3、mysql -uroot -p //此时直接回车，既可以进入数据库。

出现mysql>就说明已经进入到mysql数据库

[root@yanlei ~]# mysql -uroot -p
Enter password: 
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 2
Server version: 5.5.65-MariaDB MariaDB Server

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

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

MariaDB [(none)]> 

4、进数据库后，use mysql //选择mysql这个库，因为mysql的root密码存放在这个数据库里

MariaDB [(none)]> use mysql;

5.show tables //查看下mysql库里有哪些表，需要操作的用户名密码都在user表里。

MariaDB [mysql]> show tables;
+---------------------------+
| Tables_in_mysql           |
+---------------------------+
| columns_priv              |
| db                        |
| event                     |
| func                      |
| general_log               |
| help_category             |
| help_keyword              |
| help_relation             |
| help_topic                |
| host                      |
| ndb_binlog_index          |
| plugin                    |
| proc                      |
| procs_priv                |
| proxies_priv              |
| servers                   |
| slow_log                  |
| tables_priv               |
| time_zone                 |
| time_zone_leap_second     |
| time_zone_name            |
| time_zone_transition      |
| time_zone_transition_type |
| user                      |
+---------------------------+
24 rows in set (0.00 sec)

6.desc user //查看下user表有哪些字段

MariaDB [mysql]> desc user;
+------------------------+-----------------------------------+------+-----+---------+-------+
| Field                  | Type                              | Null | Key | Default | Extra |
+------------------------+-----------------------------------+------+-----+---------+-------+
| Host                   | char(60)                          | NO   | PRI |         |       |
| User                   | char(16)                          | NO   | PRI |         |       |
| Password               | char(41)                          | NO   |     |         |       |
| Select_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Insert_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Update_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Delete_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Create_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Drop_priv              | enum('N','Y')                     | NO   |     | N       |       |
| Reload_priv            | enum('N','Y')                     | NO   |     | N       |       |
| Shutdown_priv          | enum('N','Y')                     | NO   |     | N       |       |
| Process_priv           | enum('N','Y')                     | NO   |     | N       |       |
| File_priv              | enum('N','Y')                     | NO   |     | N       |       |
| Grant_priv             | enum('N','Y')                     | NO   |     | N       |       |
| References_priv        | enum('N','Y')                     | NO   |     | N       |       |
| Index_priv             | enum('N','Y')                     | NO   |     | N       |       |
| Alter_priv             | enum('N','Y')                     | NO   |     | N       |       |
| Show_db_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Super_priv             | enum('N','Y')                     | NO   |     | N       |       |
| Create_tmp_table_priv  | enum('N','Y')                     | NO   |     | N       |       |
| Lock_tables_priv       | enum('N','Y')                     | NO   |     | N       |       |
| Execute_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Repl_slave_priv        | enum('N','Y')                     | NO   |     | N       |       |
| Repl_client_priv       | enum('N','Y')                     | NO   |     | N       |       |
| Create_view_priv       | enum('N','Y')                     | NO   |     | N       |       |
| Show_view_priv         | enum('N','Y')                     | NO   |     | N       |       |
| Create_routine_priv    | enum('N','Y')                     | NO   |     | N       |       |
| Alter_routine_priv     | enum('N','Y')                     | NO   |     | N       |       |
| Create_user_priv       | enum('N','Y')                     | NO   |     | N       |       |
| Event_priv             | enum('N','Y')                     | NO   |     | N       |       |
| Trigger_priv           | enum('N','Y')                     | NO   |     | N       |       |
| Create_tablespace_priv | enum('N','Y')                     | NO   |     | N       |       |
| ssl_type               | enum('','ANY','X509','SPECIFIED') | NO   |     |         |       |
| ssl_cipher             | blob                              | NO   |     | NULL    |       |
| x509_issuer            | blob                              | NO   |     | NULL    |       |
| x509_subject           | blob                              | NO   |     | NULL    |       |
| max_questions          | int(11) unsigned                  | NO   |     | 0       |       |
| max_updates            | int(11) unsigned                  | NO   |     | 0       |       |
| max_connections        | int(11) unsigned                  | NO   |     | 0       |       |
| max_user_connections   | int(11)                           | NO   |     | 0       |       |
| plugin                 | char(64)                          | NO   |     |         |       |
| authentication_string  | text                              | NO   |     | NULL    |       |
+------------------------+-----------------------------------+------+-----+---------+-------+
42 rows in set (0.00 sec)

7.update user set password=password(***) where user=“root”; //用户选root,可以随便更改成任意密码

MariaDB [mysql]> update user set password = password('123456') where user = "root";
Query OK, 4 rows affected (0.00 sec)
Rows matched: 4  Changed: 4  Warnings: 0

8.flush privileges; //刷新下密码，使更改的生效。

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

9.exit //退出数据库

MariaDB [mysql]> exit
Bye
[root@yanlei ~]# 

10.mysql -uroot -p //回车输入刚刚更改的密码，就能进去了
然后再次进入配置文件vi /etc/my.cnf 把skip-grant-tables去掉

[root@yanlei ~]# mysql -uroot -p
Enter password: 
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 4
Server version: 5.5.65-MariaDB MariaDB Server

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

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

MariaDB [(none)]> 

实例

1.搭建mysql服务

[root@yanlei ~]# yum -y install mariadb*
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: mirrors.cn99.com
 * extras: mirrors.cn99.com
 * updates: mirrors.cn99.com
Resolving Dependencies
--> Running transaction check
---> Package mariadb.x86_64 1:5.5.65-1.el7 will be installed
---> Package mariadb-bench.x86_64 1:5.5.65-1.el7 will be installed
--> Processing Dependency: perl(GD) for package: 1:mariadb-bench-5.5.65
[root@yanlei ~]# systemctl enable --now mariadb
[root@yanlei ~]# systemctl restart mariadb
[root@yanlei ~]# ss -tanl
State       Recv-Q Send-Q        Local Address:Port                       Peer Address:Port              
LISTEN      0      50                        *:3306                                  *:*                  
LISTEN      0      128                       *:22                                    *:*                  
LISTEN      0      100               127.0.0.1:25                                    *:*       

2.创建一个以yanlei名字的数据库，并创建一张表student，该表包含三个字段（id，name，age），

MariaDB [yanlei]> create table student(id int primary key auto_increment not null,name varchar(50) not null,age tinyint);
Query OK, 0 rows affected (0.00 sec)

MariaDB [yanlei]> show tables
    -> ;
+------------------+
| Tables_in_yanlei |
+------------------+
| student          |
+------------------+
1 row in set (0.00 sec)

MariaDB [yanlei]> desc student
    -> ;
+-------+-------------+------+-----+---------+----------------+
| Field | Type        | Null | Key | Default | Extra          |
+-------+-------------+------+-----+---------+----------------+
| id    | int(11)     | NO   | PRI | NULL    | auto_increment |
| name  | varchar(50) | NO   |     | NULL    |                |
| age   | tinyint(4)  | YES  |     | NULL    |                |
+-------+-------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

3.查看下该新建的表有无内容（用select语句）

MariaDB [yanlei]> select * from student;
Empty set (0.00 sec)

4.往新建的student表中插入数据（用insert语句），

MariaDB [yanlei]> insert into student (id,name,age) value(1,'tom',20);
Query OK, 1 row affected (0.00 sec)
MariaDB [yanlei]> insert into student (id,name,age) value(2,'jerry',23),(3,'wangqing',25),(4,'sea',28),(5,'z
Query OK, 5 rows affected (0.00 sec)
Records: 5  Duplicates: 0  Warnings: 0

MariaDB [yanlei]> insert into student (id,name,age) values(7,'lisi',null),(8,'chenshuo',10),(9,'wangwu',3),(
Query OK, 5 rows affected (0.00 sec)
Records: 5  Duplicates: 0  Warnings: 0

MariaDB [yanlei]> select * from student;
+----+-------------+------+
| id | name        | age  |
+----+-------------+------+
|  1 | tom         |   20 |
|  2 | jerry       |   23 |
|  3 | wangqing    |   25 |
|  4 | sea         |   28 |
|  5 | zhangshan   |   26 |
|  6 | zhangshan   |   20 |
|  7 | lisi        | NULL |
|  8 | chenshuo    |   10 |
|  9 | wangwu      |    3 |
| 10 | qiuyi       |   15 |
| 11 | qiuxiaotian |   20 |
+----+-------------+------+
11 rows in set (0.00 sec)

5.修改lisi的年龄为50

MariaDB [yanlei]> update student set age = 50 where name = 'lisi';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [yanlei]> select * from student;
+----+-------------+------+
| id | name        | age  |
+----+-------------+------+
|  1 | tom         |   20 |
|  2 | jerry       |   23 |
|  3 | wangqing    |   25 |
|  4 | sea         |   28 |
|  5 | zhangshan   |   26 |
|  6 | zhangshan   |   20 |
|  7 | lisi        |   50 |
|  8 | chenshuo    |   10 |
|  9 | wangwu      |    3 |
| 10 | qiuyi       |   15 |
| 11 | qiuxiaotian |   20 |
+----+-------------+------+
11 rows in set (0.00 sec)

6.以age字段降序排序

MariaDB [yanlei]> select * from student order by age desc;
+----+-------------+------+
| id | name        | age  |
+----+-------------+------+
|  7 | lisi        |   50 |
|  4 | sea         |   28 |
|  5 | zhangshan   |   26 |
|  3 | wangqing    |   25 |
|  2 | jerry       |   23 |
|  1 | tom         |   20 |
|  6 | zhangshan   |   20 |
| 11 | qiuxiaotian |   20 |
| 10 | qiuyi       |   15 |
|  8 | chenshuo    |   10 |
|  9 | wangwu      |    3 |
+----+-------------+------+
11 rows in set (0.00 sec)

7.查询student表中年龄最小的3位同学跳过前2位

MariaDB [yanlei]> select * from student order by age limit 2,1;
+----+-------+------+
| id | name  | age  |
+----+-------+------+
| 10 | qiuyi |   15 |
+----+-------+------+
1 row in set (0.00 sec)

8.查询student表中年龄最大的4位同学

MariaDB [yanlei]> select * from student order by age desc limit 4;
+----+-----------+------+
| id | name      | age  |
+----+-----------+------+
|  7 | lisi      |   50 |
|  4 | sea       |   28 |
|  5 | zhangshan |   26 |
|  3 | wangqing  |   25 |
+----+-----------+------+
4 rows in set (0.00 sec)

9.查询student表中名字叫zhangshan的记录

MariaDB [yanlei]> select * from student where name = 'zhangshan';
+----+-----------+------+
| id | name      | age  |
+----+-----------+------+
|  5 | zhangshan |   26 |
|  6 | zhangshan |   20 |
+----+-----------+------+
2 rows in set (0.00 sec)

10.查询student表中名字叫zhangshan且年龄大于20岁的记录

MariaDB [yanlei]> select * from student where age > 20 and name = 'zhangshan';
+----+-----------+------+
| id | name      | age  |
+----+-----------+------+
|  5 | zhangshan |   26 |
+----+-----------+------+
1 row in set (0.00 sec)

11.查询student表中年龄在23到30之间的记录

MariaDB [yanlei]> select * from student where age between 23 and 30;
+----+-----------+------+
| id | name      | age  |
+----+-----------+------+
|  2 | jerry     |   23 |
|  3 | wangqing  |   25 |
|  4 | sea       |   28 |
|  5 | zhangshan |   26 |
+----+-----------+------+
4 rows in set (0.00 sec)

12.修改wangwu的年龄为100

MariaDB [yanlei]> update student set age = 100 where name = 'wangwu';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [yanlei]> select * from student where name = 'wangwu';
+----+--------+------+
| id | name   | age  |
+----+--------+------+
|  9 | wangwu |  100 |
+----+--------+------+
1 row in set (0.00 sec)

13.删除student中名字叫zhangshan且年龄小于等于20的记录

MariaDB [yanlei]> select * from student where age <= 20 and name = 'zhangshan';
+----+-----------+------+
| id | name      | age  |
+----+-----------+------+
|  6 | zhangshan |   20 |
+----+-----------+------+
1 row in set (0.00 sec)