MySQL基础，且必须提供数据，不能

文章由LinuxBoy分享于2023-03-24 08:03:55热评（185）

MySQL基础，且必须提供数据，不能

MySQL基础

MySQL基础
- 1.关系型数据库介绍
  - 1.1 数据结构模型
  - 1.2 RDBMS专用名词
  - 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配置
- 3.mysql的层序组成
  - 3.1 mysql工具使用
  - 3.2 服务器监听的两种socket地址
- 4.mysql数据类型
  - 4.1 数值类型
  - 4.2 日期和时间类型
  - 4.3 字符串类型
- 5.mysql数据库操作
  - 5.1 DDL操作
    - 5.1.1 数据库操作
    - 5.1.2 表操作
    - 5.1.3 用户操作
    - 5.1.4 查看命令show
    - 5.1.5 如何获取帮助
  - 5.2DML操作
    - 5.2.1 INSERT语句
    - 5.2.2 SELECT语句
    - 5.2.3 update语句
    - 5.2.4 delete语句
    - 5.2.5 truncate语句
  - 5.3 DCL操作
    - 5.3.1 创建权限grant
    - 5.3.2 查看授权
    - 5.3.3 取消授权revoke
- 实战案例

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
关键模型

关系模型：

二维关系：row，columm

数据库管理系统：

DBMS （DataBase Managment System）

关系：relational

关系型数据库管理系统：RDBMS

1.2 RDBMS专用名词

关系型数据库管理系统：

mysql：5.7版本之间都是开源 8.0后开始商业化

MySQL：MySQL，MariaDB，Percona-Server，sqlserver，MSsql（micresoft sql）
PostgreSQL：简称为pgsql
Oracle
MSSQL

非关系型数据库管理系统：

数据存放在内存当中变量 key=value

mongodb
redis
memcache

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 SELECT:查询表中数据
DCL	GRANT:授权 REVOKE:移除授权

2.mysql安装与配置

2.1 mysql安装

mysql安装方式有三种：

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

mysql安装步骤

[root@localhost ~]# wget http://dev.mysql.com/get/mysql57-community-release-el7-11.noarch.rpm
[root@localhost ~]# rpm -Uvh  mysql57-community-release-el7-11.noarch.rpm
[root@localhost ~]# yum module disable mysql  //禁用mysql
[root@localhost ~]# yum -y install mysql-community-server mysql-community-client  mysql-community-common mysql-community-devel  --nogpgcheck		//下载一个服务端，客户端，命令行，软件包			//--nogpgche禁止进行gpgcheck

2.2 mysql配置

安装完后设置开机自启动

[root@localhost ~]# systemctl enable --now mysqld
[root@localhost ~]# systemctl status mysqld
● mysqld.service - MySQL Server
   Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled)
   Active: active (running) since Mon 2022-07-25 14:34:30 CST; 8s ago
     Docs: man:mysqld(8)
           http://dev.mysql.com/doc/refman/en/using-systemd.html
  Process: 70174 ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.p>
  Process: 70022 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, status=0/SUCCESS)
 Main PID: 70176 (mysqld)
    Tasks: 27 (limit: 23457)
   Memory: 300.4M
   CGroup: /system.slice/mysqld.service
           └─70176 /usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid

Jul 25 14:34:28 localhost.localdomain systemd[1]: Starting MySQL Server...
Jul 25 14:34:30 localhost.localdomain systemd[1]: Started MySQL Server.

查看3306端口是否监听

[root@localhost ~]# ss -anlt | grep 3306
LISTEN 0      80                 *:3306            *:*

在日志中找出密码

[root@localhost ~]# grep "password"  /var/log/mysqld.log 
2022-07-25T06:34:28.883599Z 1 [Note] A temporary password is generated for root@localhost: OFU+amdhV3Wr			//临时密码
2022-07-25T06:35:33.642430Z 0 [Note] Shutting down plugin 'validate_password'
2022-07-25T06:35:34.759663Z 0 [Note] Shutting down plugin 'sha256_password'
2022-07-25T06:35:34.759665Z 0 [Note] Shutting down plugin 'mysql_native_password'

使用临时密码登录MySQL

[root@localhost ~]# mysql -uroot -pOFU+amdhV3Wr		//-p后可以跟密码
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 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> 				//看到这样的标识表示登录进去了

修改mysql登录密码

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

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

mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY '123456';
Query OK, 0 rows affected (0.00 sec)

为避免mysql自动升级，需要卸载最开始安装的yum源

[root@localhost ~]# rpm -e mysql57-community-release

3.mysql的层序组成

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 //套接字
    -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
    -S 			//使用套接字连接，仅限于用于本地通讯

示例

//查看当前MySQL的版本
[root@localhost ~]# mysql -V		
mysql  Ver 14.14 Distrib 5.7.38, for Linux (x86_64) using  EditLine wrapper

//指定服务器主机，默认为localhost，推荐使用ip地址 //套接字
[root@localhost ~]# mysql -uroot -p123456 -h127.0.0.1 		
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 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@localhost ~]# mysql -uroot -p -h127.0.0.1
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> 

//不登录mysql执行sql语句后退出，常用于脚本
[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	说明
ip socket	默认监听在tcp3306端口，支持远程通信
unix	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数据类型

MySQL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。

4.1 数值类型

MySQL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)。
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

类型	大小	范围（有符号）	范围（无符号）	用途
TINYINT	1 byte	(-128,127)	(0,255)	小整数值
SMALLINT	2 bytes	(-32 768，32 767)	(0，65 535)	大整数值
MEDIUMINT	3 bytes	(-8 388 608，8 388 607)	(0，4 294 967 295)	大整数值
INT或INTEGER	4 bytes	(-2 147 483 648，2 147 483 647)	(0，4 294 967 295)	大整数值
BIGINT	8 bytes	(-9,223,372,036,854,775,808，9 223 372 036 854 775 807)	(0，18 446 744 073 709 551 615)	极大整数值
FLOAT	4 bytes	(-3.402 823 466 E+38，-1.175 494 351 E-38)，0，(1.175 494 351 E-38，3.402 823 466 351 E+38)	0，(1.175 494 351 E-38，3.402 823 466 E+38)	单精度浮点数值
DOUBLE	8 bytes	(-1.797 693 134 862 315 7 E+308，-2.225 073 858 507 201 4 E-308)，0，(2.225 073 858 507 201 4 E-308，1.797 693 134 862 315 7 E+308)	0，(2.225 073 858 507 201 4 E-308，1.797 693 134 862 315 7 E+308)	双精度浮点数值
DECIMAL	对DECIMAL(M,D) ，如果M>D，为M+2否则为D+2	依赖于M和D的值	依赖于M和D的值	小点数

4.2 日期和时间类型

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。

类型	大小（byte）	范围	格式	用途
DATE	3	1000-01-01/9999-12-31	YYYY-MM-DD	日期值
TIME	3	'-838:59:59'/'838:59:59'	HH:MM:SS	时间值或持续时间
YEAR	1	1901/2155	YYYY	年份值
DATETIME	8	1000-01-01 00:00:00/9999-12-31 23:59:59	YYYY-MM-DD HH:MM:SS	混合日期和时间值
TIMESTAMP	4	1970-01-01 00:00:00/2038 结束时间是第 2147483647 秒，北京时间 2038-1-19 11:14:07，格林尼治时间 2038年1月19日凌晨 03:14:07	YYYYMMDD HHMMSS	混合日期和时间值，时间戳

4.3 字符串类型

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。

类型	大小	用途
CHAR	0-255 bytes	定长字符串
VARCHAR	0-65535 bytes	变长字符串
TINYBLOB	0-255 bytes	不超过 255 个字符的二进制字符串
TINYTEXT	0-255 bytes	短文本字符串
BLOB	0-65 535 bytes	二进制形式的长文本数据
TEXT	0-65 535 bytes	长文本数据
MEDIUMBLOB	0-16 777 215 bytes	二进制形式的中等长度文本数据
MEDIUMTEXT	0-16 777 215 bytes	中等长度文本数据
LONGBLOB	0-4 294 967 295 bytes	二进制形式的极大文本数据
LONGTEXT	0-4 294 967 295 bytes	极大文本数据

注意：char(n) 和 varchar(n) 中括号中 n 代表字符的个数，并不代表字节个数，比如 CHAR(30) 就可以存储 30 个字符。

CHAR 和 VARCHAR 类型类似，但它们保存和检索的方式不同。它们的最大长度和是否尾部空格被保留等方面也不同。在存储或检索过程中不进行大小写转换。
BINARY 和 VARBINARY 类似于 CHAR 和 VARCHAR，不同的是它们包含二进制字符串而不要非二进制字符串。也就是说，它们包含字节字符串而不是字符字符串。这说明它们没有字符集，并且排序和比较基于列值字节的数值值。
BLOB 是一个二进制大对象，可以容纳可变数量的数据。有 4 种 BLOB 类型：TINYBLOB、BLOB、MEDIUMBLOB 和 LONGBLOB。它们区别在于可容纳存储范围不同。
有 4 种 TEXT 类型：TINYTEXT、TEXT、MEDIUMTEXT 和 LONGTEXT。对应的这 4 种 BLOB 类型，可存储的最大长度不同，可根据实际情况选择。

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

[root@localhost ~]# mysql -uroot -p		//先进入MySQL数据库
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 10
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> show databases;		//查看数据库
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0.00 sec)
	
mysql> create database zxr;				//创建数据库
Query OK, 1 row affected (0.00 sec)

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

删除数据库

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

mysql> drop database zxr;				//删除数据库
Query OK, 0 rows affected (0.00 sec)

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

5.1.2 表操作

创建表之前需要进入一个数据库

mysql> create database zxr;			//需要先创建一个数据库
Query OK, 1 row affected (0.00 sec)

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

mysql> use zxr;		//进入数据库里
Database changed	//进入成功

mysql> create table linux (id int not null ,name varchar(100) not null,age tinyint);		//创建表
Query OK, 0 rows affected (0.01 sec)

mysql> show tables;			//查看表
+---------------+
| Tables_in_zxr |
+---------------+
| linux         |
+---------------+
1 row in set (0.00 sec)

删除表

mysql> show tables;
+---------------+
| Tables_in_zxr |
+---------------+
| linux         |
+---------------+
1 row in set (0.00 sec)

mysql> drop table linux;			//drop删除
Query OK, 0 rows affected (0.00 sec)

mysql> show tables;
Empty set (0.00 sec)

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

host值可以为

IP地址，如127.0.0.1
通配符
- %：配置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

创建用户

数据库用户创建语法：CREATE USER 'username'@'host' [IDENTIFIED BY 'password'];

[root@localhost ~]# mysql -uroot -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 12
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> create user 'zxr'@'127.0.0.1' identified by '123456';	//创建用户
Query OK, 0 rows affected (0.00 sec)

使用新创建的用户和密码登录mysql

[root@localhost ~]# mysql -uzxr -p123456 -h127.0.0.1
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 13
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>

删除用户

[root@localhost ~]# mysql -uroot -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 14
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> drop user 'zxr'@'127.0.0.1';			//删除用户
Query OK, 0 rows affected (0.00 sec)

mysql>

5.1.4 查看命令show

查看支持的所有字符

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 |

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 |
| mysql              |
| performance_schema |
| sys                |
| zxr                |
+--------------------+
5 rows in set (0.01 sec)

不进入数据库而列出其包含的所有表

mysql> show tables from zxr;
+---------------+
| Tables_in_zxr |
+---------------+
| linux         |
+---------------+
1 row in set (0.00 sec)

查看表结构

mysql> desc zxr.linux;
+-------+--------------+------+-----+---------+-------+
| 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 (0.03 sec)

查看表的创建命令

mysql> show create table zxr.linux;
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                           |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------+
| linux | CREATE TABLE `linux` (
  `id` int(11) NOT NULL,
  `name` varchar(100) NOT NULL,
  `age` tinyint(4) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

查看表的状态

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

mysql> use zxr;		//进入数据库
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> show table status like 'linux'\G
*************************** 1. row ***************************
           Name: linux
         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 16:00:38
    Update_time: NULL
     Check_time: NULL
      Collation: latin1_swedish_ci
       Checksum: NULL
 Create_options: 
        Comment: 
1 row in set (0.00 sec)

5.1.5 如何获取帮助

语法：HELP keyword;

示例

mysql> help create database;
Name: 'CREATE DATABASE'
Description:
Syntax:
CREATE {DATABASE | SCHEMA} [IF NOT EXISTS] db_name
    [create_option] ...

create_option: [DEFAULT] {
    CHARACTER SET [=] charset_name
  | COLLATE [=] collation_name
}

CREATE DATABASE creates a database with the given name. To use this
statement, you need the CREATE privilege for the database. CREATE
SCHEMA is a synonym for CREATE DATABASE.

URL: https://dev.mysql.com/doc/refman/5.7/en/create-database.html

5.2DML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

mysql> use zxr;
Database changed
mysql> insert into linux (id,name,age)values(2,'jerry',23),(3,'lisi',25),(4,'zhangsan',30),(5,'zhangsan',20),(6,'wangwu',null);		//一次可以插入多条记录
Query OK, 5 rows affected (0.00 sec)
Records: 5  Duplicates: 0  Warnings: 0

mysql> select * from linux;
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  2 | jerry    |   23 |
|  3 | lisi     |   25 |
|  4 | zhangsan |   30 |
|  5 | zhangsan |   20 |
|  6 | wangwu   | NULL |
+----+----------+------+
5 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，当表明很长时可以用别名来代替

示例

mysql> select id from linux;
+----+
| id |
+----+
|  2 |
|  3 |
|  4 |
|  5 |
|  6 |
+----+
5 rows in set (0.00 sec)

mysql> select * from linux;			
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  2 | jerry    |   23 |
|  3 | lisi     |   25 |
|  4 | zhangsan |   30 |
|  5 | zhangsan |   20 |
|  6 | wangwu   | NULL |
+----+----------+------+
5 rows in set (0.00 sec)

mysql> select id as 序号,name as 姓名 from linux;		//临时修改
+--------+----------+
| 序号   | 姓名     |
+--------+----------+
|      2 | jerry    |
|      3 | lisi     |
|      4 | zhangsan |
|      5 | zhangsan |
|      6 | wangwu   |
+--------+----------+
5 rows in set (0.00 sec)

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

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

示例

mysql> select * from linux;
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  2 | jerry    |   23 |
|  3 | lisi     |   25 |
|  4 | zhangsan |   30 |
|  5 | zhangsan |   20 |
|  6 | wangwu   | NULL |
+----+----------+------+
5 rows in set (0.00 sec)

mysql> select * from linux where age = 23;
+----+-------+------+
| id | name  | age  |
+----+-------+------+
|  2 | jerry |   23 |
+----+-------+------+
1 row in set (0.00 sec)

mysql> select * from linux where name like '%z%';
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  4 | zhangsan |   30 |
|  5 | zhangsan |   20 |
+----+----------+------+
2 rows in set (0.00 sec)

mysql> select * from linux where  age is not null;
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  2 | jerry    |   23 |
|  3 | lisi     |   25 |
|  4 | zhangsan |   30 |
|  5 | zhangsan |   20 |
+----+----------+------+
4 rows in set (0.00 sec)

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

mysql> select * from linux where id = 4 and age = 30;
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  4 | zhangsan |   30 |
+----+----------+------+
1 row in set (0.00 sec)

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

示例

mysql> select * from linux order by age;	//升序
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  6 | wangwu   | NULL |
|  5 | zhangsan |   20 |
|  2 | jerry    |   23 |
|  3 | lisi     |   25 |
|  4 | zhangsan |   30 |
+----+----------+------+
5 rows in set (0.00 sec)

mysql> select * from linux order by age desc;		//降序
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  4 | zhangsan |   30 |
|  3 | lisi     |   25 |
|  2 | jerry    |   23 |
|  5 | zhangsan |   20 |
|  6 | wangwu   | NULL |
+----+----------+------+
5 rows in set (0.00 sec)

mysql> select * from linux order by id limit 2;
+----+-------+------+
| id | name  | age  |
+----+-------+------+
|  2 | jerry |   23 |
|  3 | lisi  |   25 |
+----+-------+------+
2 rows in set (0.00 sec)

mysql> select * from linux order by id limit 1,2;
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  3 | lisi     |   25 |
|  4 | zhangsan |   30 |
+----+----------+------+
2 rows in set (0.00 sec)

5.2.3 update语句

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 linux;
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  2 | jerry    |   23 |
|  3 | lisi     |   25 |
|  4 | zhangsan |   30 |
|  5 | zhangsan |   20 |
|  6 | wangwu   | NULL |
+----+----------+------+
5 rows in set (0.00 sec)

mysql> update linux set age=30 where name = 'zhangsan';
Query OK, 1 row affected (0.00 sec)
Rows matched: 2  Changed: 1  Warnings: 0

mysql> select * from linux;
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  2 | jerry    |   23 |
|  3 | lisi     |   25 |
|  4 | zhangsan |   30 |
|  5 | zhangsan |   30 |
|  6 | wangwu   | NULL |
+----+----------+------+
5 rows in set (0.00 sec)

5.2.4 delete语句

语法：DELETE FROM table_name [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n];

mysql> select * from linux;
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  2 | jerry    |   23 |
|  3 | lisi     |   25 |
|  4 | zhangsan |   30 |
|  5 | zhangsan |   30 |
|  6 | wangwu   | NULL |
+----+----------+------+
5 rows in set (0.00 sec)

mysql> delete from linux where id = 5;		//删除一条记录
Query OK, 1 row affected (0.00 sec)

mysql> select * from linux;
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  2 | jerry    |   23 |
|  3 | lisi     |   25 |
|  4 | zhangsan |   30 |
|  6 | wangwu   | NULL |
+----+----------+------+
4 rows in set (0.00 sec)

mysql> delete from linux;
Query OK, 4 rows affected (0.00 sec)

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

mysql> desc linux;
+-------+--------------+------+-----+---------+-------+
| 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)

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 linux;
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  2 | jerry    |   23 |
|  3 | lisi     |   25 |
|  4 | zhangsan |   30 |
|  5 | zhangsan |   20 |
|  6 | wangwu   | NULL |
+----+----------+------+
5 rows in set (0.00 sec)

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

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

mysql> desc linux;
+-------+--------------+------+-----+---------+-------+
| 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)

5.3 DCL操作

5.3.1 创建权限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。

如有有报错需要重置一下密码

mysql> grant all on *.* to 'zxr'@'localhost' identified by '123456';
ERROR 1819 (HY000): Your password does not satisfy the current policy requirements

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

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

mysql> alter user 'root'@'localhost' identified by '123456';
Query OK, 0 rows affected (0.00 sec)

示例

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

mysql>  grant all on *.* to 'zxr'@'192.168.111.135' identified by '123
456';
Query OK, 0 rows affected, 1 warning (0.00 sec)

//授权wangqing用户在172.16.12.129上远程登录访问wangqingge数据库
mysql> grant all on zxr.* to 'zxr'@'192.168.111.137' 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 'zxr'@'%' identified by '123456';
Query OK, 0 rows affected, 1 warning (0.00 sec)

//授权root用户允许远程登录
mysql> grant all on *.* to 'root'@'192.168.111.135' identified by '123456';
Query OK, 0 rows affected, 1 warning (0.00 sec)
[root@localhost ~]# systemctl stop firewalld
[root@localhost ~]# systemctl disable firewalld
Removed /etc/systemd/system/multi-user.target.wants/firewalld.service.
Removed /etc/systemd/system/dbus-org.fedoraproject.FirewallD1.service.
mysql> grant all on *.* to 'root'@'192.168.111.1' identified by '123456';
Query OK, 0 rows affected, 1 warning (0.00 sec)

5.3.2 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)

查看指定用户的授权信息

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

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

mysql> show grants for 'zxr'@'192.168.111.135';
+--------------------------------------------------------+
| Grants for zxr@192.168.111.135                         |
+--------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'zxr'@'192.168.111.135' |
+--------------------------------------------------------+
1 row in set (0.00 sec)

mysql> show grants for 'root'@'192.168.111.135';
+---------------------------------------------------------+
| Grants for root@192.168.111.135                         |
+---------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'root'@'192.168.111.135' |
+---------------------------------------------------------+
1 row in set (0.00 sec)

5.3.3 取消授权revoke

mysql> REVOKE ALL ON *.* FROM 'zxr'@'192.168.111.135';
Query OK, 0 rows affected (0.00 sec)

mysql> FLUSH PRIVILEGES;
Query OK, 0 rows affected (0.00 sec)

注意：mysql服务进程启动时会读取mysql库中的所有授权表至内存中：

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

mysql> FLUSH PRIVILEGES;		//刷新规则

实战案例

1.搭建mysql服务

下载mysql

[root@localhost ~]# wget http://dev.mysql.com/get/mysql57-community-release-el7-11.noarch.rpm
[root@localhost ~]# rpm -Uvh  mysql57-community-release-el7-11.noarch.rpm
[root@localhost ~]# yum module disable mysql  //禁用mysql
[root@localhost ~]# yum -y install mysql-community-server mysql-community-client  mysql-community-common mysql-community-devel  --nogpgcheck		//下载一个服务端，客户端，命令行，软件包			//--nogpgche禁止进行gpgcheck

安装完后设置开机自启动

[root@localhost ~]# systemctl enable --now mysqld
[root@localhost ~]# systemctl status mysqld
● mysqld.service - MySQL Server
   Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled)
   Active: active (running) since Mon 2022-07-25 14:34:30 CST; 8s ago
     Docs: man:mysqld(8)
           http://dev.mysql.com/doc/refman/en/using-systemd.html
  Process: 70174 ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.p>
  Process: 70022 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, status=0/SUCCESS)
 Main PID: 70176 (mysqld)
    Tasks: 27 (limit: 23457)
   Memory: 300.4M
   CGroup: /system.slice/mysqld.service
           └─70176 /usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid

Jul 25 14:34:28 localhost.localdomain systemd[1]: Starting MySQL Server...
Jul 25 14:34:30 localhost.localdomain systemd[1]: Started MySQL Server.

查看3306端口是否监听

[root@localhost ~]# ss -anlt | grep 3306
LISTEN 0      80                 *:3306            *:*

在日志中找出密码

[root@localhost ~]# grep "password"  /var/log/mysqld.log 
2022-07-25T06:34:28.883599Z 1 [Note] A temporary password is generated for root@localhost: OFU+amdhV3Wr			//临时密码
2022-07-25T06:35:33.642430Z 0 [Note] Shutting down plugin 'validate_password'
2022-07-25T06:35:34.759663Z 0 [Note] Shutting down plugin 'sha256_password'
2022-07-25T06:35:34.759665Z 0 [Note] Shutting down plugin 'mysql_native_password'

使用临时密码登录MySQL

[root@localhost ~]# mysql -uroot -pOFU+amdhV3Wr		//-p后可以跟密码
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 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> 				//看到这样的标识表示登录进去了

修改mysql登录密码

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

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

mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY '123456';
Query OK, 0 rows affected (0.00 sec)

2.创建一个以你名字为名的数据库，并创建一张表student，该表包含三个字段（id，name，age），表结构如下：

mysql> desc student;
+-------+--------------+------+-----+---------+----------------+
| Field | Type         | Null | Key | Default | Extra          |
+-------+--------------+------+-----+---------+----------------+
| id    | int(11)      | NO   | PRI | NULL    | auto_increment |
| name  | varchar(100) | NO   |     | NULL    |                |
| age   | tinyint(4)   | YES  |     | NULL    |                |
+-------+--------------+------+-----+---------+----------------+
3 rows in set (0.01 sec)

解析

mysql> create database zxr;
Query OK, 1 row affected (0.00 sec)

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

mysql> use zxr;
Database changed
mysql> create table student(id int(11) primary key auto_increment,name varchar(100) not null,age tinyint(4));
Query OK, 0 rows affected (0.01 sec)

mysql> desc student;
+-------+--------------+------+-----+---------+----------------+
| Field | Type         | Null | Key | Default | Extra          |
+-------+--------------+------+-----+---------+----------------+
| id    | int(11)      | NO   | PRI | NULL    | auto_increment |
| name  | varchar(100) | 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）

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

4.往新建的student表中插入数据（用insert语句），结果应如下所示：

+----+-------------+------+
| id | name        | age  |
+----+-------------+------+
|  1 | tom         |   20 |
|  2 | jerry       |   23 |
|  3 | wangqing    |   25 |
|  4 | sean        |   28 |
|  5 | zhangshan   |   26 |
|  6 | zhangshan   |   20 |
|  7 | lisi        | NULL |
|  8 | chenshuo    |   10 |
|  9 | wangwu      |    3 |
| 10 | qiuyi       |   15 |
| 11 | qiuxiaotian |   20 |
+----+-------------+------+

解析

mysql> insert into student (name,age)values('tom',20),('jerry',23),('wangqing',25),('sean',28),('zhangshan',26),('zhangsan',20),('lisi',null),('chenshuo',10),('wangwu',3),('qiuyi',15),('qiuxiaotian',20);
Query OK, 11 rows affected (0.00 sec)
Records: 11  Duplicates: 0  Warnings: 0

mysql> select * from student;
+----+-------------+------+
| id | name        | age  |
+----+-------------+------+
|  1 | tom         |   20 |
|  2 | jerry       |   23 |
|  3 | wangqing    |   25 |
|  4 | sean        |   28 |
|  5 | zhangshan   |   26 |
|  6 | zhangsan    |   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

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

mysql> select * from student where name = 'lisi';
+----+------+------+
| id | name | age  |
+----+------+------+
|  7 | lisi |   50 |
+----+------+------+
1 row in set (0.00 sec)

6.以age字段降序排序

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

mysql> select * from student order by age desc;
+----+-------------+------+
| id | name        | age  |
+----+-------------+------+
|  7 | lisi        |   50 |
|  4 | sean        |   28 |
|  5 | zhangshan   |   26 |
|  3 | wangqing    |   25 |
|  2 | jerry       |   23 |
|  1 | tom         |   20 |
|  6 | zhangsan    |   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

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

mysql> select * from student order by age limit 2,3;
+----+-------------+------+
| id | name        | age  |
+----+-------------+------+
| 10 | qiuyi       |   15 |
|  1 | tom         |   20 |
| 11 | qiuxiaotian |   20 |
+----+-------------+------+
3 rows in set (0.00 sec)

8.查询student表中年龄最大的4位同学

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

mysql> select * from student order by age desc limit 4;
+----+-----------+------+
| id | name      | age  |
+----+-----------+------+
|  7 | lisi      |   50 |
|  4 | sean      |   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

mysql> select * from student where name = 'zhangshan';
+----+-----------+------+
| id | name      | age  |
+----+-----------+------+
|  5 | zhangshan |   26 |
+----+-----------+------+
1 row 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

mysql> select * from student where name = 'zhangshan' and age > 20;
+----+-----------+------+
| 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

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

mysql> select * from student where age >= 23 and age <= 30;
+----+-----------+------+
| id | name      | age  |
+----+-----------+------+
|  2 | jerry     |   23 |
|  3 | wangqing  |   25 |
|  4 | sean      |   28 |
|  5 | zhangshan |   26 |
+----+-----------+------+
4 rows in set (0.00 sec)

12.修改wangwu的年龄为100

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

mysql> 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

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

mysql> delete from student where name = 'zhangshan' and age >= 20;
Query OK, 1 row affected (0.00 sec)

mysql> select * from student;
+----+-------------+------+
| id | name        | age  |
+----+-------------+------+
|  1 | tom         |   20 |
|  2 | jerry       |   23 |
|  3 | wangqing    |   25 |
|  4 | sean        |   28 |
|  6 | zhangsan    |   20 |
|  7 | lisi        |   50 |
|  8 | chenshuo    |   10 |
|  9 | wangwu      |  100 |
| 10 | qiuyi       |   15 |
| 11 | qiuxiaotian |   20 |
+----+-------------+------+
10 rows in set (0.00 sec)

推荐文章：

MySQL基础，且必须提供数据，不能