1. 关系型数据库介绍
1.1 数据结构模型
数据结构模型主要有：
层次模型
网状结构
关系模型
关系模型：
二维关系：row，column
数据库管理系统：DBMS
关系：Relational，RDBMS
1.2 RDBMS专业名词
常见的关系型数据库管理系统：
MySQL：MySQL，MariaDB，Percona-Server
PostgreSQL：简称为pgsql
Oracle
MSSQL
事务：多个操作被当作一个整体对待就称为一个事务
要看一个关系型数据库是否支持事务，需要看其是否支持并满足ACID测试
ACID：ACID是事务的一个基本标准
A：Automicity，原子性
C：Consistency，一致性
I：Isolation，隔离性
D：Durability，持久性
SQL：Structure Query Language，结构化查询语言
约束：constraint，向数据表提供的数据要遵守的限制
主键约束：一个或多个字段的组合，填入的数据必须能在本表中唯一标识本行。且必须提供数据，不能为空（NOT NULL）。
一个表只能存在一个
惟一键约束：一个或多个字段的组合，填入的数据必须能在本表中唯一标识本行。允许为空（NULL）
一个表可以存在多个
外键约束：一个表中的某字段可填入数据取决于另一个表的主键已有的数据
检查性约束
索引：将表中的一个或多个字段中的数据复制一份另存，并且这些数据需要按特定次序排序存储
关系运算：
选择：挑选出符合条件的行（部分行）
投影：挑选出需要的字段
连接
数据抽象方式：
物理层：决定数据的存储格式，即RDBMS在磁盘上如何组织文件
逻辑层：描述DB存储什么数据，以及数据间存在什么样的关系
视图层：描述DB中的部分数据
1.3 关系型数据库的常见组件
关系型数据库的常见组件有：
数据库：database
表：table，由行（row）和列（column）组成
索引：index
视图：view
用户：user
权限：privilege
存储过程：procedure
存储函数：function
触发器：trigger
事件调度器：event scheduler
1.4 SQL语句
SQL语句有三种类型：
DDL：Data Defination Language，数据定义语言
DML：Data Manipulation Language，数据操纵语言
DCL：Data Control Language，数据控制语言
SQL语句类型 对应操作
DDL CREATE：创建
DROP：删除
ALTER：修改
DML INSERT：向表中插入数据
DELETE：删除表中数据
UPDATE：更新表中数据
SELECT：查询表中数据
DCL GRANT：授权
REVOKE：移除授权
2. mysql安装与配置
2.1 mysql安装
mysql安装方式有三种：
源代码：编译安装
二进制格式的程序包：展开至特定路径，并经过简单配置后即可使用
程序包管理器管理的程序包：
rpm：有两种
OS Vendor：操作系统发行商提供的
项目官方提供的
deb
//配置mysql的yum源
[root@localhost ~]# cd /usr/src/
[root@localhost src]# ls
debug kernels
[root@localhost src]# wget http://dev.mysql.com/get/mysql57-community-release-el7-10.noarch.rpm
下载过程略
[root@localhost src]# ls
debug kernels mysql57-community-release-el7-10.noarch.rpm
[root@localhost src]# yum -y install mysql57-community-release-el7-10.noarch.rpm
Loaded plugins: fastestmirror, product-id, search-disabled-repos, subscription-
: manager
This system is not registered with an entitlement server. You can use subscription-manager to register.
Examining mysql57-community-release-el7-10.noarch.rpm: mysql57-community-release-el7-10.noarch
....
Installed:
mysql57-community-release.noarch 0:el7-10
Complete!
[root@localhost ~]# ls /etc/yum.repos.d/
mysql-community.repo mysql-community-source.repo
//安装mysql5.7
[root@localhost ~]# yum -y install mysql-community-server mysql-community-client mysql-community-common mysql-community-devel
Loaded plugins: fastestmirror, product-id, search-disabled-repos, subscription-
: manager
This system is not registered with an entitlement server. You can use subscription-manager to register.
Loading mirror speeds from cached hostfile
Resolving Dependencies
--> Running transaction check
---> Package mysql-community-client.x86_64 0:5.7.23-1.el7 will be installed
--> Processing Dependency: mysql-community-libs(x86-64) >= 5.7.9 for package: mysql-community-client-5.7.23-1.el7.x86_64
....
Installed:
mysql-community-client.x86_64 0:5.7.23-1.el7
mysql-community-common.x86_64 0:5.7.23-1.el7
mysql-community-devel.x86_64 0:5.7.23-1.el7
mysql-community-libs.x86_64 0:5.7.23-1.el7
mysql-community-libs-compat.x86_64 0:5.7.23-1.el7
mysql-community-server.x86_64 0:5.7.23-1.el7
Replaced:
mariadb-libs.x86_64 1:5.5.56-2.el7
Complete!
2.2 mysql配置
//启动mysql
[root@localhost ~]# systemctl start 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 Sun 2018-08-12 23:39:33 CST; 6s ago
Docs: man:mysqld(8)
http://dev.mysql.com/doc/refman/en/using-systemd.html
Process: 1325 ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid $MYSQLD_OPTS (code=exited, status=0/SUCCESS)
Process: 1249 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, status=0/SUCCESS)
Main PID: 1327 (mysqld)
CGroup: /system.slice/mysqld.service
└─1327 /usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/my...
Aug 12 23:39:26 localhost.localdomain systemd[1]: Starting MySQL Server...
Aug 12 23:39:33 localhost.localdomain systemd[1]: Started MySQL Server.
//确保3306端口已经监听起来
[root@localhost ~]# ss -antl
State Recv-Q Send-Q Local Address:Port Peer Address:Port
LISTEN 0 128 *:22 *:*
LISTEN 0 100 127.0.0.1:25 *:*
LISTEN 0 128 :::22 :::*
LISTEN 0 100 ::1:25 :::*
LISTEN 0 80 :::3306 :::*
//在日志文件中找出临时密码
[root@localhost ~]# grep "password" /var/log/mysqld.log
2018-08-12T15:39:28.710830Z 1 [Note] A temporary password is generated for root@localhost: &vsD!YuKT7&/
//此处的临时密码为&vsD!YuKT7&/
//注意，你的密码跟这是不一样的，一定要看清楚，禁止直接复制我这里的密码
//使用获取到的临时密码登录mysql
[root@localhost ~]# mysql -uroot -p
Enter password: //此处输入密码，可以直接复制你的密码粘贴至此处，也可手动输入
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.7.23
Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> //看到有这样的标识符则表示成功登录了
//修改mysql登录密码
mysql> set global validate_password_policy=0;
Query OK, 0 rows affected (0.00 sec)
mysql> set global validate_password_length=1;
Query OK, 0 rows affected (0.01 sec)
mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY '123456';
Query OK, 0 rows affected (0.00 sec)
mysql> quit
Bye
//为避免mysql自动升级，这里需要卸载最开始安装的yum源
[root@localhost ~]# rpm -qa|grep mysql
mysql-community-server-5.7.23-1.el7.x86_64
mysql57-community-release-el7-10.noarch
mysql-community-common-5.7.23-1.el7.x86_64
mysql-community-client-5.7.23-1.el7.x86_64
mysql-community-libs-compat-5.7.23-1.el7.x86_64
mysql-community-libs-5.7.23-1.el7.x86_64
mysql-community-devel-5.7.23-1.el7.x86_64
[root@localhost ~]# yum -y remove mysql57-community-release-el7-10.noarch
Loaded plugins: fastestmirror, product-id, search-disabled-repos, subscription-
: manager
This system is not registered with an entitlement server. You can use subscription-manager to register.
Resolving Dependencies
--> Running transaction check
....
Removed:
mysql57-community-release.noarch 0:el7-10
Complete!
3. mysql的程序组成
客户端
mysql：CLI交互式客户端程序
mysql_secure_installation：安全初始化，强烈建议安装完以后执行此命令
mysqldump：mysql备份工具
mysqladmin
服务器端
mysqld
3.1 mysql工具使用
//语法：mysql [OPTIONS] [database]
//常用的OPTIONS：
-uUSERNAME //指定用户名，默认为root
-hHOST //指定服务器主机，默认为localhost，推荐使用ip地址
-pPASSWORD //指定用户的密码
-P# //指定数据库监听的端口，这里的#需用实际的端口号代替，如-P3307
-V //查看当前使用的mysql版本
-e //不登录mysql执行sql语句后退出，常用于脚本
[root@localhost ~]# mysql -V
mysql Ver 14.14 Distrib 5.7.28, for Linux (x86_64) using EditLine wrapper
[root@localhost ~]# mysql -uroot -p123456 -h192.168.136.133
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: 5.7.28 MySQL Community Server (GPL)
Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>
//注意，不推荐直接在命令行里直接用-pPASSWORD的方式登录，而是使用-p选项，然后交互式输入密码
[root@localhost ~]# mysql -uroot -p -h192.168.136.133
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 7
Server version: 5.7.28 MySQL Community Server (GPL)
Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>
[root@localhost ~]# mysql -uroot -p -h192.168.136.133 -e 'SHOW DATABASES;'
Enter password:
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| sys |
+--------------------+
3.2 服务器监听的两种socket地址
socket类型 说明
ip socket 默认监听在tcp的3306端口，支持远程通信
unix sock 监听在sock文件上（/tmp/mysql.sock，/var/lib/mysql/mysql.sock）
仅支持本地通信
server地址只能是：localhost，127.0.0.1
4. mysql数据库操作
4.1 DDL操作
4.1.1 数据库操作
//创建数据库
//语法：create database [if not exists] 'DB_NAME';
//创建数据库liping
mysql> create database liping;
Query OK, 1 row affected (0.07 sec)
//查看当前实例有哪些数据库
mysql> show databases
-> ;
+--------------------+
| Database |
+--------------------+
| information_schema |
| liping |
| mysql |
| performance_schema |
| sys |
+--------------------+
5 rows in set (0.00 sec)
//删除数据库
//语法：drop database [if exists] 'DB_NAME';
//删除数据库liping
mysql> drop database liping;
Query OK, 0 rows affected (0.10 sec)
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| sys |
+--------------------+
4 rows in set (0.00 sec)
4.1.2 表操作
//创建表 //语法：create table table_name (col1 datatype 修饰符,col2 datatype 修饰符) ENGINE='存储引擎类型'; //在数据库liping里创建表student mysql> create database liping; //创建数据库liping Query OK, 1 row affected (0.00 sec) mysql> use liping; //进入liping数据库 Database changed mysql> create table student (id int not null,name varchar(100) not null,age tinyint); //创建student表 Query OK, 0 rows affected (0.28 sec) mysql> show tables; //查看当前数据库有哪些表 +------------------+ | Tables_in_liping | +------------------+ | student | +------------------+ 1 row in set (0.00 sec) //删除表 //语法：drop table [ if exists] 'table_name'; //删除表student mysql> show tables; +------------------+ | Tables_in_liping | +------------------+ | student | +------------------+ 1 row in set (0.00 sec) mysql> drop table student; Query OK, 0 rows affected (0.12 sec) mysql> show tables; Empty set (0.00 sec)
4.1.3 用户操作
mysql用户帐号由两部分组成，如'USERNAME'@'HOST'，表示此USERNAME只能从此HOST上远程登录
这里（'USERNAME'@'HOST'）的HOST用于限制此用户可通过哪些主机远程连接mysql程序，其值可为：
IP地址，如：172.16.12.129
通配符
%：匹配任意长度的任意字符，常用于设置允许从任何主机登录
_：匹配任意单个字符
//数据库用户创建 //语法：create user 'username'@'host' [identified by 'password']; //创建数据库用户liping mysql> create user 'liping'@'127.0.0.1' identified by 'Liping123!'; Query OK, 0 rows affected (0.06 sec) //使用新创建的用户和密码登录 [root@localhost ~]# mysql -uliping -pLiping123! -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 28 Server version: 5.7.28 MySQL Community Server (GPL) Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. //删除数据库用户 //语法：drop user 'username'@'host'; mysql> drop user 'liping'@'127.0.0.1'; Query OK, 0 rows affected (0.05 sec)
4.1.4 查看命令show
mysql> show character set; //查看支持的所有字符集
+----------+---------------------------------+---------------------+--------+
| Charset | Description | Default collation | Maxlen |
+----------+---------------------------------+---------------------+--------+
| big5 | Big5 Traditional Chinese | big5_chinese_ci | 2 |
| dec8 | DEC West European | dec8_swedish_ci | 1 |
| cp850 | DOS West European | cp850_general_ci | 1 |
| hp8 | HP West European | hp8_english_ci | 1 |
| koi8r | KOI8-R Relcom Russian | koi8r_general_ci | 1 |
| latin1 | cp1252 West European | latin1_swedish_ci | 1 |
| latin2 | ISO 8859-2 Central European | latin2_general_ci | 1 |
| swe7 | 7bit Swedish | swe7_swedish_ci | 1 |
mysql> show engines \G //查看当前数据库支持的所有存储引擎
*************************** 1. row ***************************
Engine: InnoDB
Support: DEFAULT
Comment: 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
mysql> show databases; //查看数据库信息
+--------------------+
| Database |
+--------------------+
| information_schema |
| liping |
| mysql |
| performance_schema |
| sys |
+--------------------+
5 rows in set (0.00 sec)
mysql> show tables from liping; //不进入某数据库而列出其包含的所有表
+------------------+
| Tables_in_liping |
+------------------+
| student |
+------------------+
1 row in set (0.00 sec)
//查看表结构
//语法：desc [db_name.]table_name;
mysql> desc liping.student;
+-------+--------------+------+-----+---------+-------+
| 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)
//查看某表的创建命令
//语法：show create table table_name;
mysql> show create table liping.student;
+---------+----------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+---------+----------------------------------------------------------------------------------------------------------------------------------------------------------+
| student | CREATE TABLE `student` (
`id` int(11) NOT NULL,
`name` varchar(100) NOT NULL,
`age` tinyint(4) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+---------+----------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)
//查看某表的状态
//语法：show table status like 'table_name'\G
mysql> use liping //进入数据库wangqingge
Database changed
mysql> show table status like 'student'\G //查看student表的状态
*************************** 1. row ***************************
Name: student
Engine: InnoDB
Version: 10
Row_format: Dynamic
Rows: 0
Avg_row_length: 0
Data_length: 16384
Max_data_length: 0
Index_length: 0
Data_free: 0
Auto_increment: NULL
Create_time: 2019-11-18 17:58:03
Update_time: NULL
Check_time: NULL
Collation: latin1_swedish_ci
Checksum: NULL
Create_options:
Comment:
1 row in set (0.00 sec)
4.1.5 获取帮助
//获取命令使用帮助
//语法：help keyword;
mysql> help create table; //获取创建表的帮助
Name: 'CREATE TABLE'
Description:
Syntax:
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
(create_definition,...)
[table_options]
[partition_options]
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
[(create_definition,...)]
[table_options]
[partition_options]
[IGNORE | REPLACE]
[AS] query_expression
....
.....
4.2 DML操作
DML操作包括增(insert)、删(delete、改(update)、查(select)，均属针对表的操作。
4.2.1 insert语句
//DML操作之增操作insert
//语法：insert [into] table_name [(column_name,...)] {VALUES | VALUE} (value1,...),(...),...
mysql> use liping;
Database changed
mysql> insert into student (id,name,age) value (1,'tom',20); //一次插入一条记录
Query OK, 1 row affected (0.07 sec)
mysql> insert student (id,name,age) values (2,'jerry',23),(3,'wangqing',25),(4,'sean',28),(5,'zhangshan',26),(6,'zhngshan',20),(7,'lisi',null),(8,'wangwu',10),(9,'chenshuo',3),(10,'qiuyi',15),(11,'qiuxiaotian',20); //一次插入多条记录
Query OK, 10 rows affected (0.04 sec)
Records: 10 Duplicates: 0 Warnings: 0
4.2.2 select语句
字段column表示法
表示符 代表什么？
- 所有字段
as 字段别名，如col1 AS alias1
当表名很长时用别名代替
条件判断语句WHERE
操作类型 常用操作符
操作符 >，<，>=，<=，=，!=
BETWEEN column# AND column#
LIKE：模糊匹配
RLIKE：基于正则表达式进行模式匹配
IS NOT NULL：非空
IS NULL：空
条件逻辑操作 AND
OR
NOT
ORDER BY：排序，默认为升序（ASC）
ORDER BY语句 意义
ORDER BY ‘column_name' 根据column_name进行升序排序
ORDER BY 'column_name' DESC 根据column_name进行降序排序
ORDER BY ’column_name' LIMIT 2 根据column_name进行升序排序
并只取前2个结果
ORDER BY ‘column_name' LIMIT 1,2 根据column_name进行升序排序
并且略过第1个结果取后面的2个结果
//DML操作之查操作select //语法：select column1,column2,... from table_name [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n]; mysql> use liping; Database changed mysql> select * from student; //查看表的全部信息 +----+-------------+------+ | id | name | age | +----+-------------+------+ | 1 | tom | 20 | | 2 | jerry | 23 | | 3 | wangqing | 25 | | 4 | sean | 28 | | 5 | zhangshan | 26 | | 6 | zhngshan | 20 | | 7 | lisi | NULL | | 8 | wangwu | 10 | | 9 | chenshuo | 3 | | 10 | qiuyi | 15 | | 11 | qiuxiaotian | 20 | +----+-------------+------+ 11 rows in set (0.00 sec) //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) //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) //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) //查询student表中以年龄升序进行排序 mysql> select * from student order by age; +----+-------------+------+ | id | name | age | +----+-------------+------+ | 7 | lisi | NULL | | 9 | wangwu | 3 | | 8 | chenshuo | 10 | | 10 | qiuyi | 15 | | 1 | tom | 20 | | 6 | shangshan | 20 | | 11 | qiuxiaotian | 20 | | 2 | jerry | 23 | | 3 | wangqing | 25 | | 5 | zhangshan | 26 | | 4 | sean | 28 | +----+-------------+------+ 11 rows in set (0.00 sec) //查询student表中以年龄降序进行排序 mysql> select * from student order by age desc; +----+-------------+------+ | id | name | age | +----+-------------+------+ | 4 | sean | 28 | | 5 | zhangshan | 26 | | 3 | wangqing | 25 | | 2 | jerry | 23 | | 1 | tom | 20 | | 6 | shangshan | 20 | | 11 | qiuxiaotian | 20 | | 10 | qiuyi | 15 | | 8 | chenshuo | 10 | | 9 | wangwu | 3 | | 7 | lisi | NULL | +----+-------------+------+ 11 rows in set (0.00 sec) //查询student表中以年龄升序进行排序只取年龄最小的2位 mysql> select * from student order by age limit 2; +----+--------+------+ | id | name | age | +----+--------+------+ | 7 | lisi | NULL | | 9 | wangwu | 3 | +----+--------+------+ 2 rows in set (0.00 sec) //查询student表中以年龄升序进行排序忽略第一个人的取后面两个人的 mysql> select * from student order by age limit 1,2; +----+----------+------+ | id | name | age | +----+----------+------+ | 9 | wangwu | 3 | | 8 | chenshuo | 10 | +----+----------+------+ 2 rows in set (0.00 sec) //查询student表中年龄为空的 mysql> select * from student where age is null; +----+------+------+ | id | name | age | +----+------+------+ | 7 | lisi | NULL | +----+------+------+ 1 row in set (0.00 sec)
4.2.3 update语句
//DML操作之改操作update //语法：update table_name SET column1 = new_value1[,column2 = new_value2,...] [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n]; mysql> select * from student; +----+-------------+------+ | id | name | age | +----+-------------+------+ | 1 | tom | 20 | | 2 | jerry | 23 | | 3 | wangqing | 25 | | 4 | sean | 28 | | 5 | zhangshan | 26 | | 6 | shangshan | 20 | | 7 | lisi | NULL | | 8 | chenshuo | 10 | | 9 | wangwu | 3 | | 10 | qiuyi | 15 | | 11 | qiuxiaotian | 20 | +----+-------------+------+ 11 rows in set (0.00 sec) mysql> update student set age=30 where name='tom'; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> select * from student where name='tom'; +----+------+------+ | id | name | age | +----+------+------+ | 1 | tom | 30 | +----+------+------+ 1 row in set (0.00 sec)
4.2.4 delete语句
//DML操作之删操作delete //语法：delete from table_name [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n]; mysql> select * from student; +----+-------------+------+ | id | name | age | +----+-------------+------+ | 1 | tom | 30 | | 2 | jerry | 23 | | 3 | wangqing | 25 | | 4 | sean | 28 | | 5 | zhangshan | 26 | | 6 | shangshan | 20 | | 7 | lisi | NULL | | 8 | chenshuo | 10 | | 9 | wangwu | 3 | | 10 | qiuyi | 15 | | 11 | qiuxiaotian | 20 | +----+-------------+------+ 11 rows in set (0.00 sec) mysql> delete from student where id=6; Query OK, 1 row affected (0.00 sec) mysql> select * from student; +----+-------------+------+ | id | name | age | +----+-------------+------+ | 1 | tom | 30 | | 2 | jerry | 23 | | 3 | wangqing | 25 | | 4 | sean | 28 | | 5 | zhangshan | 26 | | 7 | lisi | NULL | | 8 | chenshuo | 10 | | 9 | wangwu | 3 | | 10 | qiuyi | 15 | | 11 | qiuxiaotian | 20 | +----+-------------+------+ 10 rows in set (0.00 sec)
4.2.5 truncate语句
truncate与delete的区别：
语句类型 特点
delete DELETE删除表内容时仅删除内容，但会保留表结构
DELETE语句每次删除一行，并在事务日志中为所删除的每行记录一项
可以通过回滚事务日志恢复数据
非常占用空间
truncate 删除表中所有数据，且无法恢复
表结构、约束和索引等保持不变，新添加的行计数值重置为初始值
执行速度比DELETE快，且使用的系统和事务日志资源少
通过释放存储表数据所用的数据页来删除数据，并且只在事务日志中记录页的释放
对于有外键约束引用的表，不能使用TRUNCATE TABLE删除数据
不能用于加入了索引视图的表
//语法：truncate table_name; mysql> select * from student; +----+-------------+------+ | id | name | age | +----+-------------+------+ | 1 | tom | 30 | | 2 | jerry | 23 | | 3 | wangqing | 25 | | 4 | sean | 28 | | 5 | zhangshan | 26 | | 7 | lisi | NULL | | 8 | chenshuo | 10 | | 9 | wangwu | 3 | | 10 | qiuyi | 15 | | 11 | qiuxiaotian | 20 | +----+-------------+------+ 10 rows in set (0.00 sec) mysql> truncate student; Query OK, 0 rows affected (0.00 sec) mysql> desc student; +-------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+--------------+------+-----+---------+-------+ | id | int(11) | NO | | NULL | | | name | varchar(100) | NO | | NULL | | | age | tinyint(4) | YES | | NULL | | +-------+--------------+------+-----+---------+-------+ 3 rows in set (0.00 sec)
4.3 DCL操作
4.3.1 创建授权grant
权限类型(priv_type)
权限类型 代表什么？
ALL 所有权限
SELECT 读取内容的权限
INSERT 插入内容的权限
UPDATE 更新内容的权限
DELETE 删除内容的权限
指定要操作的对象db_name.table_name
表示方式 意义
. 所有库的所有表
db_name 指定库的所有表
db_name.table_name 指定库的指定表
WITH GRANT OPTION：被授权的用户可将自己的权限副本转赠给其他用户，说白点就是将自己的权限完全复制给另一个用户。不建议使用。
grant priv_type,... ON [object_type] db_name.table_name TO ‘username'@'host' [IDENTIFIED BY 'password'] [WITH GRANT OPTION]; //授权tom用户在数据库本机上登录访问所有数据库 mysql> grant all on *.* to 'tom'@'localhost' identified by 'Liping123!'; Query OK, 0 rows affected, 1 warning (1.72 sec) mysql> grant all on *.* to 'tom'@'127.0.0.1' identified by 'Liping123!'; Query OK, 0 rows affected, 1 warning (0.00 sec) //授权tom用户在192.168.136.134上远程登录访问liping数据库 mysql> grant all on liping.* to 'tom'@'192.168.136.134' identified by 'Liping123!'; Query OK, 0 rows affected, 1 warning (0.00 sec) //授权tom用户在所有位置上远程登录访问所有数据库 mysql> grant all on *.* to 'tom'@'%' identified by 'Liping123!'; Query OK, 0 rows affected, 1 warning (0.00 sec)
4.3.2 查看授权
//查看当前登录用户的授权信息 mysql> show grants; +---------------------------------------------------------------------+ | Grants for root@localhost | +---------------------------------------------------------------------+ | GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' WITH GRANT OPTION | | GRANT PROXY ON ''@'' TO 'root'@'localhost' WITH GRANT OPTION | +---------------------------------------------------------------------+ 2 rows in set (0.00 sec) //查看指定用户tom的授权信息 mysql> show grants for tom; +------------------------------------------+ | Grants for tom@% | +------------------------------------------+ | GRANT ALL PRIVILEGES ON *.* TO 'tom'@'%' | +------------------------------------------+ 1 row in set (0.00 sec) mysql> show grants for 'tom'@'192.168.136.134'; +---------------------------------------------------------------+ | Grants for tom@192.168.136.134 | +---------------------------------------------------------------+ | GRANT USAGE ON *.* TO 'tom'@'192.168.136.134' | | GRANT ALL PRIVILEGES ON `liping`.* TO 'tom'@'192.168.136.134' | +---------------------------------------------------------------+ 2 rows in set (0.00 sec) mysql> show grants for 'tom'@'%'; +------------------------------------------+ | Grants for tom@% | +------------------------------------------+ | GRANT ALL PRIVILEGES ON *.* TO 'tom'@'%' | +------------------------------------------+ 1 row in set (0.00 sec)
4.3.3 取消授权revoke
//语法：revoke priv_type,... ON db_name.table_name FROM 'username'@'host'; mysql> revoke all on *.* from 'tom'@'192.168.136.134'; 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;