mysql基础
1. 关系型数据库介绍
1.1 数据结构模型
数据结构模型主要有：
- 层次模型
- 网状结构
- 关系模型
关系模型又分为:
- 二维关系：row(行)，column（列）
- 数据库管理系统：DBMS（database manager system）
- 关系数据库管理系统（Relational database manager system）
1.2 RDBMS专业名词
常见的关系型数据库管理系统：
- MySQL：MySQL，MariaDB（和MySQL是同源，RHEL7上yum源自带），Percona-Server
- PostgreSQL：简称为pgsql
- Oracle
- MSSQL
事务:多个操作被当作一个整体对待就称为一个事务(整个事务中的所有操作，要么全部完成，要么全部不完成，不可能停滞在中间某个环节。事务在执行过程中发生错误，会被回滚（Rollback）到事务开始前的状态，就像这个事务从来没有执行过一样。)
要看一个关系型数据库是否支持事务，需要看其是否支持并满足ACID测试
ACID:ACID是事务的一个基本标准
- A：Automicity，原子性
- C：Consistency，一致性
- I：Isolation，隔离性
- D：Durability，持久性
SQL:Structure Query Language，结构化查询语言
约束:constraint，向数据表提供的数据要遵守的限制
- 主键约束：一个或多个字段的组合，填入的数据必须能在本表中唯一标识本行。且必须提供数据，不能为空（NOT NULL）。一个表只能存在一个
- 惟一键约束：一个或多个字段的组合，填入的数据必须能在本表中唯一标识本行。允许为空（NULL）一个表可以存在多个
- 外键约束：一个表中的某字段可填入数据取决于另一个表的主键已有的数据
- 检查性约束
索引：将表中的一个或多个字段中的数据复制一份另存，并且这些数据需要按特定次序排序存储
关系运算：
- 选择：挑选出符合条件的行（部分行）
- 投影：挑选出需要的字段（一般是列）
- 连接（将两个表相关联）
数据抽象方式：
- 物理层：决定数据的存储格式，即RDBMS在磁盘上如何组织文件
- 逻辑层：描述DB存储什么数据，以及数据间存在什么样的关系
- 视图层：描述DB中的部分数据
1.3 关系型数据库的常见组件
关系型数据库的常见组件有：
- 数据库：database
- 表：table，由行（row）和列（column）组成
- 索引：index
- 视图：view
- 用户：user
- 权限：privilege
- 存储过程：procedure
- 存储函数：function
- 触发器：trigger
- 事件调度器：event scheduler
1.4 SQL语句
SQL语句有三种类型：
- DDL：Data Defination Language，数据定义语言
- DML：Data Manipulation Language，数据操纵语言
- DCL：Data Control Language，数据控制语言
| SQL语句类型 | 对应操作 |
|---|---|
| DDL | CREATE：创建 DROP:删除 ALTER：修改 |
| DML | INSERT：向表中插入数据 DELETE：删除表中数据 UPDATE：更新表中数据 SELECT：查询表中数据 |
| DCL | GRANT：授权 REVOKE：移除授权 |
2. mysql安装与配置
2.1 mysql安装
mysql安装方式有三种：
- 源代码：编译安装
- 二进制格式的程序包：展开至特定路径，并经过简单配置后即可使用
- 程序包管理器管理的程序包：
1.rpm(有两种，os Vendor，项目官方提供)
2.deb
//第一步下载mysql5.7的yum源
[root@cwh ~]# wget http://dev.mysql.com/get/mysql57-community-release-el7-10.noarch.rpm
--2019-04-22 15:04:39-- http://dev.mysql.com/get/mysql57-community-release-el7-10.noarch.rpm
...
...
2019-04-22 15:04:46 (389 KB/s) - 已保存 “mysql57-community-release-el7-10.noarch.rpm” [25548/25548])
[root@cwh ~]# ls
aaa anaconda-ks.cfg cwh4http.sh httpd.conf httpd-vhosts.conf httppz1.sh mysql57-community-release-el7-10.noarch.rpm
//第二步安装下载下来的mysql源
[root@cwh ~]# yum -y install mysql57-community-release-el7-10.noarch.rpm
[root@cwh ~]# ls /etc/yum.repos.d/
7CentOS-Base.repo mysql-community.repo mysql-community-source.repo redhat.repo
//第三步安装mysql5.7
yum -y install mysql-community-server mysql-community-client mysql-community-common mysql-community-devel
2.2 mysql基本配置
//第一步启动mysql并查看端口是否开启
[root@cwh ~]# systemctl start mysqld
[root@cwh ~]# ss -antl
State Recv-Q Send-Q Local Address:Port Peer Address:Port
LISTEN 0 128 *:22 *:*
LISTEN 0 100 127.0.0.1:25 *:*
LISTEN 0 80 :::3306 :::*
LISTEN 0 128 :::22 :::*
LISTEN 0 100 ::1:25 :::*
//第二步在mysql日志文件中找出mysql临时密码
[root@cwh ~]# cat /var/log/mysqld.log |grep password
2019-04-22T07:40:39.531315Z 1 [Note] A temporary password is generated for root@localhost: xB>aDF_l>4>;
//最后的xB>aDF_l>4>;为临时密码以后登陆时需要
//第三步使用获取到的临时密码登录mysql
[root@localhost ~]# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.7.25
Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> //这样显示出来了就表示临时登录成功
//第四步修改mysql登录密码
mysql> set global validate_password_policy=0;
Query OK, 0 rows affected (0.00 sec)
mysql> set global validate_password_length=1;
Query OK, 0 rows affected (0.00 sec)
mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY 'cwh123!';
Query OK, 0 rows affected (0.00 sec)
mysql> quit
Bye
//第五步为避免mysql自动升级，这里需要卸载最开始安装的yum源
[root@localhost ~]# rpm -qa |grep mysql
mysql-community-common-5.7.25-1.el7.x86_64
mysql-community-libs-5.7.25-1.el7.x86_64
mysql-community-libs-compat-5.7.25-1.el7.x86_64
mysql-community-server-5.7.25-1.el7.x86_64
mysql57-community-release-el7-10.noarch
mysql-community-client-5.7.25-1.el7.x86_64
mysql-community-devel-5.7.25-1.el7.x86_64
[root@localhost ~]# yum -y remove mysql57-community-release-el7-10.noarch
3. mysql的程序组成
- 客户端
- mysql：CLI交互式客户端程序
- mysql_secure_installation：安全初始化，强烈建议安装完以后执行此命令
- mysqldump：mysql备份工具
- mysqladmin
- 服务器端
- mysqld
3.1 mysql工具使用
//语法：mysql [OPTIONS] [database]
//常用的OPTIONS：
-uUSERNAME //指定用户名，默认为root
-hHOST //指定服务器主机，默认为localhost，推荐使用ip地址
-pPASSWORD //指定用户的密码
-P# //指定数据库监听的端口，这里的#需用实际的端口号代替，如-P3307
-V //查看当前使用的mysql版本
-e //不登录mysql执行sql语句后退出，常用于脚本
//查看当前使用的mysql脚本
[root@localhost ~]# mysql -V
mysql Ver 14.14 Distrib 5.7.25, for Linux (x86_64) using EditLine wrapper
//本地登录
[root@cwh ~]# mysql -uroot -pcwh123! -h127.0.0.1
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 13
Server version: 5.7.25 MySQL Community Server (GPL)
Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> //此时显示已经登陆上了
//注意，不推荐直接在命令行里直接用-pPASSWORD的方式登录，而是使用-p选项，然后交互式输入密码
[root@cwh ~]# mysql -uroot -p -h127.0.0.1
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 14
Server version: 5.7.25 MySQL Community Server (GPL)
Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>
//查看mysql中有哪些数据库
[root@localhost ~]# mysql -uroot -p -h127.0.0.1 -e 'show databases'
Enter password:
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| sys |
+--------------------+
3.2 服务器监听的两种socket地址
| socket类型 | 说明 |
|---|---|
| ip socket | 默认监听在tcp的3306端口，支持远程通信 |
| unix sock | 监听在sock文件上（/tmp/mysql.sock，/var/lib/mysql/mysql.sock 仅支持本地通信 server地址只能是：localhost，127.0.0.1 |
4. mysql数据库操作
4.1 DDL操作
4.1.1 数据库操作
//创建数据库
//语法：CREATE DATABASE [IF NOT EXISTS] 'DB_NAME';
//创建数据库chengweihong
[root@localhost ~]# mysql -uroot -p
Enter password:
mysql>
mysql> create database if not exists chengweihong;
Query OK, 1 row affected (0.00 sec)
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| chengweihong |
| mysql |
| performance_schema |
| sys |
+--------------------+
5 rows in set (0.00 sec)
//删除数据库
//语法：DROP DATABASE [IF EXISTS] 'DB_NAME';
//删除数据库chengweihong
mysql> drop database if exists chengweihong;
Query OK, 0 rows affected (0.02 sec)
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| sys |
+--------------------+
4 rows in set (0.00 sec)
4.1.2 表操作
//创建表
//语法：CREATE TABLE table_name (col1 datatype 修饰符,col2 datatype 修饰符) ENGINE='存储引擎类型';
//在数据库chengweihong里创建表cwh
//首先创建chengweihong数据库
mysql> create database chengweihong;
Query OK, 1 row affected (0.01 sec)
//在在数据库chengweihong中创建表
mysql> create table cwh(id int not null,name varchar(100),age tinyint);
Query OK, 0 rows affected (0.04 sec)
mysql> show tables;
+------------------------+
| Tables_in_chengweihong |
+------------------------+
| cwh |
+------------------------+
1 row in set (0.00 sec)
//具体查看表的内容
mysql> desc cwh;
+-------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id | int(11) | NO | | NULL | |
| name | varchar(100) | YES | | NULL | |
| age | tinyint(4) | YES | | NULL | |
+-------+--------------+------+-----+---------+-------+
3 rows in set (0.03 sec)
//删除表
//语法：DROP TABLE [ IF EXISTS ] 'table_name';
//删除表cwh
mysql> drop table if exists cwh;
Query OK, 0 rows affected (0.01 sec)
mysql> show tables;
Empty set (0.00 sec)
4.1.3 用户操作
mysql用户帐号由两部分组成,如'USERNAME'@'HOST'，表示此USERNAME只能从此HOST上远程登录
这里（'USERNAME'@'HOST'）的HOST用于限制此用户可通过哪些主机远程连接mysql程序，其值可为:
- IP地址，如：172.16.12.129
- 通配符
- %：匹配任意长度的任意字符，常用于设置允许从任何主机登录
- _：匹配任意单个字符
//数据库用户创建
//语法：CREATE USER 'username'@'host' [IDENTIFIED BY 'password'];
//创建数据库用户wangqing
mysql> create user cwh@192.168.112.149 identified by 'cwh123!';
Query OK, 0 rows affected (0.01 sec)
//在192.168.112.149上验证
[root@149 ~]# mysql -ucwh -p -h192.168.112.146
Enter password:
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MySQL connection id is 19
Server version: 5.7.25 MySQL Community Server (GPL)
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MySQL [(none)]> //因为没有配置权限所以查看的东西有限，看不到chengweihong的数据库
MySQL [(none)]> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
+--------------------+
1 row in set (0.01 sec)
//删除数据库用户
//语法：DROP USER 'username'@'host';
mysql> drop user cwh@192.168.112.149;
Query OK, 0 rows affected (0.01 sec)
//删除用户后在192.168.112.149主机上验证
[root@149 ~]# mysql -ucwh -p -h192.168.112.146
Enter password:
ERROR 1130 (HY000): Host '192.168.112.149' is not allowed to connect to this MySQL server
//可以看出已经无法登陆了
4.1.4 查看命令SHOW
//1.查看有哪些数据库
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| chengweihong |
| mysql |
| performance_schema |
| sys |
+--------------------+
5 rows in set (0.00 sec)
//2.查看数据库中有哪些表格（要看那个数据的表格就先进入到数据库中）
mysql> use chengweihong
Database changed
mysql> show tables;
+------------------------+
| Tables_in_chengweihong |
+------------------------+
| cwh |
+------------------------+
1 row in set (0.00 sec)
//3.查看支持的所有字符集
mysql> show character set;
+----------+---------------------------------+---------------------+--------+
| Charset | Description | Default collation | Maxlen |
+----------+---------------------------------+---------------------+--------+
| big5 | Big5 Traditional Chinese | big5_chinese_ci | 2 |
| dec8 | DEC West European | dec8_swedish_ci | 1 |
| cp850 | DOS West European | cp850_general_ci | 1 |
| hp8 | HP West European | hp8_english_ci | 1 |
| koi8r | KOI8-R Relcom Russian | koi8r_general_ci | 1 |
| latin1 | cp1252 West European | latin1_swedish_ci | 1 |
| latin2 | ISO 8859-2 Central European | latin2_general_ci | 1 |
| swe7 | 7bit Swedish | swe7_swedish_ci | 1 |
| ascii | US ASCII | ascii_general_ci | 1 |
| ujis | EUC-JP Japanese | ujis_japanese_ci | 3 |
| sjis | Shift-JIS Japanese | sjis_japanese_ci | 2 |
| hebrew | ISO 8859-8 Hebrew | hebrew_general_ci | 1 |
| tis620 | TIS620 Thai | tis620_thai_ci | 1 |
| euckr | EUC-KR Korean | euckr_korean_ci | 2 |
| koi8u | KOI8-U Ukrainian | koi8u_general_ci | 1 |
| gb2312 | GB2312 Simplified Chinese | gb2312_chinese_ci | 2 |
| greek | ISO 8859-7 Greek | greek_general_ci | 1 |
| cp1250 | Windows Central European | cp1250_general_ci | 1 |
| gbk | GBK Simplified Chinese | gbk_chinese_ci | 2 |
| latin5 | ISO 8859-9 Turkish | latin5_turkish_ci | 1 |
| armscii8 | ARMSCII-8 Armenian | armscii8_general_ci | 1 |
| utf8 | UTF-8 Unicode | utf8_general_ci | 3 |
| ucs2 | UCS-2 Unicode | ucs2_general_ci | 2 |
| cp866 | DOS Russian | cp866_general_ci | 1 |
| keybcs2 | DOS Kamenicky Czech-Slovak | keybcs2_general_ci | 1 |
| macce | Mac Central European | macce_general_ci | 1 |
| macroman | Mac West European | macroman_general_ci | 1 |
| cp852 | DOS Central European | cp852_general_ci | 1 |
| latin7 | ISO 8859-13 Baltic | latin7_general_ci | 1 |
| utf8mb4 | UTF-8 Unicode | utf8mb4_general_ci | 4 |
| cp1251 | Windows Cyrillic | cp1251_general_ci | 1 |
| utf16 | UTF-16 Unicode | utf16_general_ci | 4 |
| utf16le | UTF-16LE Unicode | utf16le_general_ci | 4 |
| cp1256 | Windows Arabic | cp1256_general_ci | 1 |
| cp1257 | Windows Baltic | cp1257_general_ci | 1 |
| utf32 | UTF-32 Unicode | utf32_general_ci | 4 |
| binary | Binary pseudo charset | binary | 1 |
| geostd8 | GEOSTD8 Georgian | geostd8_general_ci | 1 |
| cp932 | SJIS for Windows Japanese | cp932_japanese_ci | 2 |
| eucjpms | UJIS for Windows Japanese | eucjpms_japanese_ci | 3 |
| gb18030 | China National Standard GB18030 | gb18030_chinese_ci | 4 |
+----------+---------------------------------+---------------------+--------+
41 rows in set (0.01 sec)
//4.查看当前数据库支持的所有存储引擎
mysql> show engines;
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine | Support | Comment | Transactions | XA | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| InnoDB | DEFAULT | Supports transactions, row-level locking, and foreign keys | YES | YES | YES |
| MRG_MYISAM | YES | Collection of identical MyISAM tables | NO | NO | NO |
| MEMORY | YES | Hash based, stored in memory, useful for temporary tables | NO | NO | NO |
| BLACKHOLE | YES | /dev/null storage engine (anything you write to it disappears) | NO | NO | NO |
| MyISAM | YES | MyISAM storage engine | NO | NO | NO |
| CSV | YES | CSV storage engine | NO | NO | NO |
| ARCHIVE | YES | Archive storage engine | NO | NO | NO |
| PERFORMANCE_SCHEMA | YES | Performance Schema | NO | NO | NO |
| FEDERATED | NO | Federated MySQL storage engine | NULL | NULL | NULL |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
9 rows in set (0.00 sec)
//5.不进入某数据库而列出其包含的所有表
mysql> show tables from chengweihong;
+------------------------+
| Tables_in_chengweihong |
+------------------------+
| cwh |
+------------------------+
1 row in set (0.00 sec)
//6.查看表结构
//语法：DESC [db_name.]table_name;
mysql> desc chengweihong.cwh;
+-------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id | int(11) | NO | | NULL | |
| name | varchar(100) | YES | | NULL | |
| age | tinyint(4) | YES | | NULL | |
+-------+--------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
//7.查看某表的创建命令
//语法：SHOW CREATE TABLE table_name;
mysql> show create table cwh;
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------+
| cwh | CREATE TABLE `cwh` (
`id` int(11) NOT NULL,
`name` varchar(100) DEFAULT NULL,
`age` tinyint(4) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
//查看某表的状态
//语法：SHOW TABLE STATUS LIKE 'table_name'\G
mysql> show create table cwh\G;
*************************** 1. row ***************************
Table: cwh
Create Table: CREATE TABLE `cwh` (
`id` int(11) NOT NULL,
`name` varchar(100) DEFAULT NULL,
`age` tinyint(4) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
4.1.5 获取帮助
//获取创建表的帮助
mysql> help create table
Name: 'CREATE TABLE'
Description:
Syntax:
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
(create_definition,...)
[table_options]
[partition_options]
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
[(create_definition,...)]
[table_options]
[partition_options]
[IGNORE | REPLACE]
[AS] query_expression
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
{ LIKE old_tbl_name | (LIKE old_tbl_name) }
4.2 DML操作（数据操控语言）
DML操作包括增(INSERT)、删(DELETE)、改(UPDATE)、查(SELECT)，均属针对表的操作。
4.2.1 INSERT语句
1.一次插入一条完整数据
mysql> insert into cwh value(1,'tom',10);
Query OK, 1 row affected (0.01 sec)
mysql> select * from cwh;
+----+------+------+
| id | name | age |
+----+------+------+
| 1 | tom | 10 |
+----+------+------+
1 row in set (0.00 sec)
2.一次插入多条完整数据
mysql> insert into cwh values(2,'jerry',20),(3,'natasha',30)
-> ; //因为最后没有输入分号
Query OK, 2 rows affected (0.01 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> select * from cwh
-> ; //因为ui后没输入；
+----+---------+------+
| id | name | age |
+----+---------+------+
| 1 | tom | 10 |
| 2 | jerry | 20 |
| 3 | natasha | 30 |
+----+---------+------+
3 rows in set (0.00 sec)
3.一次插入一条指定字段的数据
mysql> insert into cwh(id,name) value(4,'aaa');
Query OK, 1 row affected (0.00 sec)
mysql> select * from cwh;
+----+---------+------+
| id | name | age |
+----+---------+------+
| 1 | tom | 10 |
| 2 | jerry | 20 |
| 3 | natasha | 30 |
| 4 | aaa | NULL |
+----+---------+------+
4 rows in set (0.00 sec)
4.一次插入多条指定字段的数据
mysql> insert into cwh(id,name) values(5,'bbb'),(6,'ccc');
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> select * from cwh
-> ;
+----+---------+------+
| id | name | age |
+----+---------+------+
| 1 | tom | 10 |
| 2 | jerry | 20 |
| 3 | natasha | 30 |
| 4 | aaa | NULL |
| 5 | bbb | NULL |
| 6 | ccc | NULL |
+----+---------+------+
6 rows in set (0.00 sec)
4.2.2 SELECT语句
字段column表示法
| 表示符 | 表示 |
|---|---|
| * | 所有字段 |
| as | 字段别名, 当名字很长时用别名代替 |
条件判断语句WHERE
| 操作类型 | 常用操作符 |
|---|---|
| 操作符 | >，<，>=，<=，=，!= BETWEEN column# AND column# LIKE：模糊匹配 RLIKE：基于正则表达式进行模式匹配 IS NOT NULL：非空 IS NULL：空 |
| 条件逻辑操作 | AND,OR,NOT |
ORDER BY：排序，默认为升序（ASC）
| ORDER BY语句 | 意义 |
|---|---|
| ORDER BY 'column_name' | 根据column_name进行升序排序 |
| ORDER BY 'column_name'DESC | 根据column_name进行降序排序 |
| ORDER BY ’column_name' LIMIT 2 | 根据column_name进行升序排序 并只取前2个结果 |
| ORDER BY ‘column_name' LIMIT 1,2 | 根据column_name进行升序排序并且略过第1个结果取后面的2个结果 |
//DML操作之查操作select
//语法：SELECT column1,column2,... FROM table_name [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n];
1.查看表的所有内容
mysql> select * from cwh;
+----+---------+------+
| id | name | age |
+----+---------+------+
| 1 | tom | 10 |
| 2 | jerry | 20 |
| 3 | natasha | 30 |
| 4 | aaa | NULL |
| 5 | bbb | NULL |
| 6 | ccc | NULL |
+----+---------+------+
6 rows in set (0.00 sec)
2.按字段查看表的内容
mysql> select name from cwh;
+---------+
| name |
+---------+
| tom |
| jerry |
| natasha |
| aaa |
| bbb |
| ccc |
+---------+
6 rows in set (0.00 sec)
3.查看表的内容并按某字段升序排序
mysql> select * from cwh order by age;
+----+---------+------+
| id | name | age |
+----+---------+------+
| 4 | aaa | NULL |
| 5 | bbb | NULL |
| 6 | ccc | NULL |
| 1 | tom | 10 |
| 2 | jerry | 20 |
| 3 | natasha | 30 |
+----+---------+------+
6 rows in set (0.00 sec)
4.查看表的内容按升序排序取前两个
mysql> select * from cwh order by id limit 2;
+----+-------+------+
| id | name | age |
+----+-------+------+
| 1 | tom | 10 |
| 2 | jerry | 20 |
+----+-------+------+
2 rows in set (0.00 sec)
5.查看表的内容按升序排序跳过第一个取后两个
mysql> select * from cwh order by id limit 1,2;
+----+---------+------+
| id | name | age |
+----+---------+------+
| 2 | jerry | 20 |
| 3 | natasha | 30 |
+----+---------+------+
2 rows in set (0.00 sec)
6.查看表的内容只打印age大于25的信息
mysql> select * from cwh where age >=25;
+----+---------+------+
| id | name | age |
+----+---------+------+
| 3 | natasha | 30 |
+----+---------+------+
1 row in set (0.00 sec)
7.查看表的内容只打印age=25和name=tom的信息
mysql> select * from cwh where age=10 and name='tom';
+----+------+------+
| id | name | age |
+----+------+------+
| 1 | tom | 10 |
+----+------+------+
1 row in set (0.00 sec)
8.查看表格打印id在2-4之间的信息
mysql> select * from cwh where id between 2 and 4;
+----+---------+------+
| id | name | age |
+----+---------+------+
| 2 | jerry | 20 |
| 3 | natasha | 30 |
| 4 | aaa | NULL |
+----+---------+------+
3 rows in set (0.00 sec)
9.查看表格打印age为空的信息
mysql> select * from cwh where age is null;
+----+------+------+
| id | name | age |
+----+------+------+
| 4 | aaa | NULL |
| 5 | bbb | NULL |
| 6 | ccc | NULL |
+----+------+------+
3 rows in set (0.00 sec)
10.查看表格打印age不为空的信息
mysql> select * from cwh where age is not null;
+----+---------+------+
| id | name | age |
+----+---------+------+
| 1 | tom | 10 |
| 2 | jerry | 20 |
| 3 | natasha | 30 |
+----+---------+------+
3 rows in set (0.00 sec)
4.2.3 update语句
//DML操作之改操作update
//语法：UPDATE table_name SET column1 = new_value1[,column2 = new_value2,...] [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n];
注意：此语句只能一条一条的修改记录，可以修改一条记录中的多个字段
1.修改表中的aaa的age由null改为40
mysql> update cwh set age=40 where name='aaa';
Query OK, 1 row affected (0.00 sec)
mysql> select * from cwh;
+----+---------+------+
| id | name | age |
+----+---------+------+
| 1 | tom | 10 |
| 2 | jerry | 20 |
| 3 | natasha | 30 |
| 4 | aaa | 40 |
| 5 | bbb | NULL |
| 6 | ccc | NULL |
+----+---------+------+
6 rows in set (0.00 sec)
2.修改表中一行记录中多个字段将id=6的ccc改为cwh，age改为60
mysql> update cwh set name='cwh',age=60 where id=6;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from cwh;
+----+---------+------+
| id | name | age |
+----+---------+------+
| 1 | tom | 10 |
| 2 | jerry | 20 |
| 3 | natasha | 30 |
| 4 | aaa | 40 |
| 5 | bbb | NULL |
| 6 | cwh | 60 |
+----+---------+------+
6 rows in set (0.00 sec)
4.2.4 delete语句
//DML操作之删操作delete
//语法：DELETE FROM table_name [WHERE clause] [ORDER BY 'column_name' [DESC]] [LIMIT [m,]n];
1.删除某条记录
mysql> select * from cwh;
+----+---------+------+
| id | name | age |
+----+---------+------+
| 1 | tom | 10 |
| 2 | jerry | 20 |
| 3 | natasha | 30 |
| 4 | aaa | 40 |
| 5 | bbb | NULL |
| 6 | cwh | 60 |
+----+---------+------+
6 rows in set (0.00 sec)
mysql> delete from cwh where id=5;
Query OK, 1 row affected (0.00 sec)
mysql> select * from cwh;
+----+---------+------+
| id | name | age |
+----+---------+------+
| 1 | tom | 10 |
| 2 | jerry | 20 |
| 3 | natasha | 30 |
| 4 | aaa | 40 |
| 6 | cwh | 60 |
+----+---------+------+
5 rows in set (0.00 sec)
2.删除整个表的内容
mysql> select * from cwh111;
+----+------+------+
| id | name | age |
+----+------+------+
| 1 | qqq | 10 |
| 2 | www | 20 |
+----+------+------+
2 rows in set (0.00 sec)
mysql> delete from cwh111;
Query OK, 2 rows affected (0.00 sec)
mysql> select * from cwh111;
Empty set (0.00 sec)
4.2.5 truncate语句
truncate与delete的区别:
| 语句类型 | 特点 |
|---|---|
| delete | DELETE删除表内容时仅删除内容，但会保留表结构 DELETE语句每次删除一行，并在事务日志中为所删除的每行记录一项 可以通过回滚事务日志恢复数据 非常占用空间 |
| truncate | 删除表中所有数据，且无法恢复 表结构、约束和索引等保持不变，新添加的行计数值重置为初始值 执行速度比DELETE快，且使用的系统和事务日志资源少 通过释放存储表数据所用的数据页来删除数据，并且只在事务日志中记录页的释放 对于有外键约束引用的表，不能使用TRUNCATE TABLE删除数据 不能用于加入了索引视图的表 |
mysql> select * from cwh111;
+----+------+------+
| id | name | age |
+----+------+------+
| 1 | qqq | 10 |
| 2 | www | 20 |
+----+------+------+
2 rows in set (0.00 sec)
mysql> truncate cwh111;
Query OK, 0 rows affected (0.01 sec)
mysql> select * from cwh111;
Empty set (0.00 sec)
4.3 DCL操作
4.3.1 创建授权grant
权限类型(priv_type)
| 权限类型 | 代表什么? |
|---|---|
| ALL | 所有权限 |
| SELECT | 读取内容的权限 |
| INSERT | 插入内容的权限 |
| UPDATE | 更新内容的权限 |
| DELETE | 删除内容的权限 |
指定要操作的对象db_name.table_name
| 表示方式 | 意义 |
|---|---|
| *.* | 所有库的所有表 |
| db_name | 指定库的所有表 |
| db_name.table_name | 指定库的指定表 |
WITH GRANT OPTION：被授权的用户可将自己的权限副本转赠给其他用户，说白点就是将自己的权限完全复制给另一个用户。不建议使用。
语法：GRANT priv_type,... ON [object_type] db_name.table_name TO ‘username'@'host' [IDENTIFIED BY 'password'] [WITH GRANT OPTION];
1.授权cwh用户在数据库本机上登录访问所有数据库
mysql> grant all on *.* to cwh@127.0.0.1 identified by '+7p6Mg2JsHgX1bIaOSwSykG8O2M='; //此处密码使用openssl rand 20 -base64 生成
mysql> show grants for cwh@127.0.0.1
-> ;
+--------------------------------------------------+
| Grants for cwh@127.0.0.1 |
+--------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'cwh'@'127.0.0.1' |
+--------------------------------------------------+
1 row in set (0.00 sec)
2.授权cwh用户在192.168.112.149上远程登录访问chengweihong数据库
//首先授权
mysql> grant all on chengweihong.* to cwh@192.168.112.149 identifiied by '+7p6Mg2JsHgX1bIaOSwSykG8O2M=';
Query OK, 0 rows affected, 1 warning (0.00 sec)
//在查看授权内容
mysql> show grants for cwh@192.168.112.149;
+---------------------------------------------------------------------+
| Grants for cwh@192.168.112.149 |
+---------------------------------------------------------------------+
| GRANT USAGE ON *.* TO 'cwh'@'192.168.112.149' |
| GRANT ALL PRIVILEGES ON `chengweihong`.* TO 'cwh'@'192.168.112.149' |
+---------------------------------------------------------------------+
2 rows in set (0.00 sec)
//最后在192.168.112.149主机上验证
[root@146 ~]# mysql -ucwh -p -h192.168.112.146
Enter password:
MySQL [(none)]> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| chengweihong |
+--------------------+
2 rows in set (0.00 sec)
MySQL [chengweihong]> show tables;
+------------------------+
| Tables_in_chengweihong |
+------------------------+
| cwh |
| cwh111 |
+------------------------+
2 rows in set (0.00 sec)
3.授权cwh用户在所有位置上远程登录访问chengweihong数据库的cwh表
//首先授权
mysql> grant all on chengweihong.cwh to 'cwh'@'%' identified by '+7p6Mg2JsHgX1bIaOSwSykG8O2M=';
Query OK, 0 rows affected, 1 warning (0.00 sec)
//在查看权限
mysql> show grants for cwh@'%';
+-----------------------------------------------------------+
| Grants for cwh@% |
+-----------------------------------------------------------+
| GRANT USAGE ON *.* TO 'cwh'@'%' |
| GRANT ALL PRIVILEGES ON `chengweihong`.`cwh` TO 'cwh'@'%' |
+-----------------------------------------------------------+
2 rows in set (0.00 sec)
//在146主机上验证
[root@146 ~]# mysql -ucwh -p -h192.168.112.146
Enter password:
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MySQL connection id is 11
Server version: 5.7.25 MySQL Community Server (GPL)
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MySQL [(none)]> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| chengweihong |
+--------------------+
2 rows in set (0.00 sec)
MySQL [(none)]> show tables from chengweihong;
+------------------------+
| Tables_in_chengweihong |
+------------------------+
| cwh |
+------------------------+
1 row in set (0.00 sec)
4.3.2 查看授权
1.查看当前登录用户的授权信息
mysql> show grants;
+---------------------------------------------------------------------+
| Grants for root@localhost |
+---------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' WITH GRANT OPTION |
| GRANT PROXY ON ''@'' TO 'root'@'localhost' WITH GRANT OPTION |
+---------------------------------------------------------------------+
2 rows in set (0.00 sec)
2.查看指定用户cwh的授权信息
mysql> show grants for cwh@'%';
+-----------------------------------------------------------+
| Grants for cwh@% |
+-----------------------------------------------------------+
| GRANT USAGE ON *.* TO 'cwh'@'%' |
| GRANT ALL PRIVILEGES ON `chengweihong`.`cwh` TO 'cwh'@'%' |
+-----------------------------------------------------------+
2 rows in set (0.00 sec)
4.3.3 取消授权REVOKE
//语法：REVOKE priv_type,... ON db_name.table_name FROM 'username'@'host';
1.取消对cwh用户的授权
mysql> revoke all on chengweihong.cwh from cwh@'%';
Query OK, 0 rows affected (0.00 sec)
mysql> show grants for cwh@'%';
+---------------------------------+
| Grants for cwh@% |
+---------------------------------+
| GRANT USAGE ON *.* TO 'cwh'@'%' |
+---------------------------------+
1 row in set (0.00 sec)
注意：mysql服务进程启动时会读取mysql库中的所有授权表至内存中：
- GRANT或REVOKE等执行权限操作会保存于表中，mysql的服务进程会自动重读授权表，并更新至内存中
- 对于不能够或不能及时重读授权表的命令，可手动让mysql的服务进程重读授权表
刷新授权表：
mysql> FLUSH PRIVILEGES;