MySQL客户端工具的使用与MySQL SQL语句

MySQL客户端工具的使用

1、MySQL程序的组成

• 客户端

  • mysql:CLI交互式客户端程序
  • mycli:CLI交互式客户端程序;使用sql语句时会有提示信息
  • 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：官方提供的shell命令行工具

• 服务器端

  • mysqld

2、MySQL监听地址

服务器监听的两种socket地址：

3、数据库配置文件

数据库配置文件为：/etc/my.cnf和/etc/my.cnf.d目录下的配置文件

//修改配置文件，配置字符编码
[root@localhost ~]# vim /etc/my.cnf
    [mysqld]
    character-set-server=utf8mb4
    collation-server=utf8mb4_general_ci

    [client]
    default-character-set=utf8mb4

    [mysql]
    default-character-set=utf8mb4

4、客户端工具的使用

//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，如-P3307
    -S              //指定套接字文件位置，多实例部署MySQL时需要使用
    -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
    --defaults-file=配置文件	//指定MySQL配置文件位置，用于加载客户端配置
    
[root@localhost ~]# mysql -V
mysql  Ver 14.14 Distrib 5.7.38, for Linux (x86_64) using  EditLine wrapper

[root@localhost ~]# mysql -uroot -pPasswd123! -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 4
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 -e 'show databases;'
Enter password: 
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| zsl                |
+--------------------+

MySQL 数据类型

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。

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)。

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。

3、字符串类型

字符串类型指CHAR、VARCHAR、BINARY、VARBINARY、BLOB、TEXT、ENUM和SET。

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。

MySQL SQL语句

1、DDL操作

1.1 数据库DDL操作

//创建数据库
//语法：create database [if not exists] 'da_name';

//创建数据库zsl
mysql> create database zsl;
Query OK, 1 row affected (0.00 sec)

//查看当前实例有哪些数据库
mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| zsl                |
+--------------------+
5 rows in set (0.00 sec)

//删除数据库
//语法：drop database [if exists] 'da_name';

//删除数据库zsl
mysql> drop database zsl;
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)

//创建数据库时,设置数据库的字符集：
//character set:指定数据库采用的字符集,utf8不能写成utf-8,建议使用utf8mb4字符集
//collate:指定数据库字符集的排序规则,utf8mb4的默认排序规则为utf8mb4_general_ci（通过show character set查看）
mysql> create database dbtest character set utf8mb4 collate utf8mb4_general_ci;

//数据库客户端字符编码需要和服务端字符集保持一致
//SET NAMES:指定客户端字符集
mysql> SET NAMES utf8mb4;

//字符集配置都可写入MySQL配置文件中启动MySQL服务时自动加载

1.2 表DDL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lsz里创建表lsztable
mysql> CREATE DATABASE IF NOT EXISTS lsz;		//创建数据库lsz
Query OK, 1 row affected (0.00 sec)

mysql> use lsz;		//进入lsz数据库
Database changed

//创建lsztable表
mysql> create table lsztable (id int(10) not null,name varchar(100) not null,age tinyint);
Query OK, 0 rows affected (0.00 sec)

//查看当前数据库有哪些表
mysql> show tables;
+---------------+
| Tables_in_lsz |
+---------------+
| lsztable      |
+---------------+
1 row in set (0.00 sec)

//删除表
//语法：drop table [ if exists ] 'table_name';

//删除表lsztable
mysql> drop table lsztable;
Query OK, 0 rows affected (0.01 sec)

mysql> show tables;
Empty set (0.00 sec)

//创建表时，设置字段、表的字符编码
mysql> create table tb_course(id int not null primary key auto_increment,course_name vaarchar(50)) default character set utf8 collate utf8_general-ci;

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用于限制此用户可通过哪些主机远程连接mysql程序。

HOST的值可为：

• 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zsl
mysql> create user 'zsl'@'127.0.0.1' identified by 'Passwd123!';
Query OK, 0 rows affected (0.00 sec)

//使用新创建的用户和密码登录
[root@localhost ~]# mysql -uzsl -pPasswd123! -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 5
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> 

//删除数据库用户
//语法：drop user 'username'@'host'; 

//删除数据库用户zsl
mysql> drop user 'zsl'@'127.0.0.1';
Query OK, 0 rows affected (0.00 sec)

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 |
......
......

mysql> show variables like '%char%';		//查看客户端的字符编码
+--------------------------------------+----------------------------+
| Variable_name                        | Value                      |
+--------------------------------------+----------------------------+
| character_set_client                 | utf8                       |
| character_set_connection             | utf8                       |
| character_set_database               | latin1                     |
| character_set_filesystem             | binary                     |
| character_set_results                | utf8                       |
| character_set_server                 | latin1                     |
| character_set_system                 | utf8                       |
| character_sets_dir                   | /usr/share/mysql/charsets/ |
| validate_password_special_char_count | 1                          |
+--------------------------------------+----------------------------+
9 rows in set (0.00 sec)

mysql> select charset(id) from lsztable;		//查看某表中某字段使用的字符编码
......
......

mysql> show engines;		//查看当前数据库支持的所有存储引擎
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine             | Support | Comment                                                        | Transactions | XA   | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| InnoDB             | DEFAULT | 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)

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

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

//查看表结构
//语法：desc [db_name.]table_name;

mysql> desc lsz.lsztable;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id    | int(10)      | 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，可以看到创建表时设置的参数
//语法：show create table table_name;

mysql> show create table lsz.lsztable;
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table    | Create Table                                                                                                                                              |
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------+
| lsztable | CREATE TABLE `lsztable` (
  `id` int(10) NOT NULL,
  `name` varchar(100) NOT NULL,
  `age` tinyint(4) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

//查看某表的状态
//语法：show table status like 'table_name'\G

mysql> show table status like 'lsztable'\G;
*************************** 1. row ***************************
           Name: lsztable
         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: 2022-07-26 08:40:01
    Update_time: NULL
     Check_time: NULL
      Collation: latin1_swedish_ci
       Checksum: NULL
 Create_options: 
        Comment: 
1 row in set (0.00 sec)

ERROR: 
No query specified

1.5 alter修改操作

//修改数据库属性
//语法：alter adtabase 'db_name' character set charset_name | collate collation_name

//修改数据库字符集为utf8
mysql> alter database lsz character set utf8;
Query OK, 1 row affected (0.01 sec)

//修改表
//语法：alter table <table_name> [option]

//给lsztable表添加新的一列，先查看表结构
mysql> desc lsztable;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id    | int(10)      | NO   |     | NULL    |       |
| name  | varchar(100) | NO   |     | NULL    |       |
| age   | tinyint(4)   | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

//给lsztable表添加一列'phone'
mysql> alter table lsztable add phone int(11);
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

//查看表结构
mysql> desc lsztable;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id    | int(10)      | NO   |     | NULL    |       |
| name  | varchar(100) | NO   |     | NULL    |       |
| age   | tinyint(4)   | YES  |     | NULL    |       |
| phone | int(11)      | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

//修改lsztable表中'phone'列为'sex'
mysql> alter table lsztable change phone sex varchar(4);
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc lsztable;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id    | int(10)      | NO   |     | NULL    |       |
| name  | varchar(100) | NO   |     | NULL    |       |
| age   | tinyint(4)   | YES  |     | NULL    |       |
| sex   | varchar(4)   | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

//修改表名为zsltable
mysql> alter table lsztable rename to zsltable;
Query OK, 0 rows affected (0.00 sec)

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

//修改数据库字符编码
mysql> altar database dbtest character set utf8 collate utf8_general_ci;

//修改表字符编码
mysql> altar table tbtest character set utf8 collate utf8_general_ci;

1.6 获取帮助

//获取命令使用帮助
//语法：help commond;

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
 ......
 ......

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。

2.1 insert语句

//DML操作之增操作insert
//语法：inster [into] table_name [(column_name,...)] {values | value} (value1,...),(...),...

mysql> use lsz;
Database changed

//一次插入一条记录
mysql> insert zsltable (id,name,age,sex) value(1,'tom',20,'nan');
Query OK, 1 row affected (0.00 sec)

//一次插入多条记录
mysql> insert zsltable (id,name,age,sex) values(2,'jerry',23,'nv'),(3,'zsl',18,'nan'),(4,'sean',null,'nv');
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

2.2 select语句

字段column匹配方式:

条件判断语句WHERE:

ORDER BY：排序，默认为升序（ASC）

/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];

#进入数据库
mysql> use lsz;
Database changed

#查看表所有的内容
mysql> select * from zsltable;
+----+-------+------+------+
| id | name  | age  | sex  |
+----+-------+------+------+
|  1 | tom   |   20 | nan  |
|  2 | jerry |   23 | nv   |
|  3 | zsl   |   18 | nan  |
|  4 | sean  | NULL | nv   |
+----+-------+------+------+
4 rows in set (0.00 sec)

#查看表的name字段内容
mysql> select name from zsltable;
+-------+
| name  |
+-------+
| tom   |
| jerry |
| zsl   |
| sean  |
+-------+
4 rows in set (0.00 sec)

#根据age字段内容从低到高排列
mysql> select * from zsltable order by age;
+----+-------+------+------+
| id | name  | age  | sex  |
+----+-------+------+------+
|  4 | sean  | NULL | nv   |
|  3 | zsl   |   18 | nan  |
|  1 | tom   |   20 | nan  |
|  2 | jerry |   23 | nv   |
+----+-------+------+------+
4 rows in set (0.00 sec)

#根据age字段内容从高到低排列
mysql> select * from zsltable order by age desc;
+----+-------+------+------+
| id | name  | age  | sex  |
+----+-------+------+------+
|  2 | jerry |   23 | nv   |
|  1 | tom   |   20 | nan  |
|  3 | zsl   |   18 | nan  |
|  4 | sean  | NULL | nv   |
+----+-------+------+------+
4 rows in set (0.00 sec)

#根据age字段内容从低到高排列取前两行
mysql> select * from zsltable order by age limit 2;
+----+------+------+------+
| id | name | age  | sex  |
+----+------+------+------+
|  4 | sean | NULL | nv   |
|  3 | zsl  |   18 | nan  |
+----+------+------+------+
2 rows in set (0.00 sec)

#根据age字段内容从低到高排列，跳过第一行取下一行
mysql> select * from zsltable order by age limit 1,1;
+----+------+------+------+
| id | name | age  | sex  |
+----+------+------+------+
|  3 | zsl  |   18 | nan  |
+----+------+------+------+
1 row in set (0.00 sec)

#查看表中年龄大于等于20的行；
mysql> select * from zsltable where age >=20;
+----+-------+------+------+
| id | name  | age  | sex  |
+----+-------+------+------+
|  1 | tom   |   20 | nan  |
|  2 | jerry |   23 | nv   |
+----+-------+------+------+
2 rows in set (0.00 sec)

#查看表中年龄大于等于20且名字叫jerry的行；
mysql> select * from zsltable where age >=20 and name = 'jerry';
+----+-------+------+------+
| id | name  | age  | sex  |
+----+-------+------+------+
|  2 | jerry |   23 | nv   |
+----+-------+------+------+
1 row in set (0.00 sec)

#查看表中年龄18到23的行
mysql> select * from zsltable where age between 18 and 23;
+----+-------+------+------+
| id | name  | age  | sex  |
+----+-------+------+------+
|  1 | tom   |   20 | nan  |
|  2 | jerry |   23 | nv   |
|  3 | zsl   |   18 | nan  |
+----+-------+------+------+
3 rows in set (0.00 sec)

#查看表中年龄不为空的
mysql> select * from zsltable where age is not null;
+----+-------+------+------+
| id | name  | age  | sex  |
+----+-------+------+------+
|  1 | tom   |   20 | nan  |
|  2 | jerry |   23 | nv   |
|  3 | zsl   |   18 | nan  |
+----+-------+------+------+
3 rows in set (0.00 sec)

#查看表中年龄为空的
mysql> select * from zsltable where age is null;
+----+------+------+------+
| id | name | age  | sex  |
+----+------+------+------+
|  4 | sean | NULL | nv   |
+----+------+------+------+
1 row in set (0.00 sec)

#查找name字段含有z的行
mysql> select * from zsltable where name like '%z%';
+----+------+------+------+
| id | name | age  | sex  |
+----+------+------+------+
|  3 | zsl  |   18 | nan  |
+----+------+------+------+
1 row in set (0.00 sec)

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 zsltable;
+----+-------+------+------+
| id | name  | age  | sex  |
+----+-------+------+------+
|  1 | tom   |   20 | nan  |
|  2 | jerry |   23 | nv   |
|  3 | zsl   |   18 | nan  |
|  4 | sean  | NULL | nv   |
+----+-------+------+------+
4 rows in set (0.00 sec)

mysql> update zsltable set age=25 where name = 'sean';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from zsltable where name = 'sean';
+----+------+------+------+
| id | name | age  | sex  |
+----+------+------+------+
|  4 | sean |   25 | nv   |
+----+------+------+------+
1 row in set (0.00 sec)

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 zsltable;
+----+-------+------+------+
| id | name  | age  | sex  |
+----+-------+------+------+
|  1 | tom   |   20 | nan  |
|  2 | jerry |   23 | nv   |
|  3 | zsl   |   18 | nan  |
|  4 | sean  |   25 | nv   |
+----+-------+------+------+
4 rows in set (0.00 sec)

mysql> delete from zsltable where id =3;		//删除某条记录
Query OK, 1 row affected (0.00 sec)

mysql> select * from zsltable;
+----+-------+------+------+
| id | name  | age  | sex  |
+----+-------+------+------+
|  1 | tom   |   20 | nan  |
|  2 | jerry |   23 | nv   |
|  4 | sean  |   25 | nv   |
+----+-------+------+------+
3 rows in set (0.00 sec)

mysql> delete from zsltable;		 //删除整张表的内容
Query OK, 3 rows affected (0.01 sec)

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

mysql> desc zsltable;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id    | int(10)      | NO   |     | NULL    |       |
| name  | varchar(100) | NO   |     | NULL    |       |
| age   | tinyint(4)   | YES  |     | NULL    |       |
| sex   | varchar(4)   | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

2.5 truncate语句

truncate与delete的区别：

//语法：TRUNCATE table_name;

mysql> select * from zsltable;
+----+-------+------+------+
| id | name  | age  | sex  |
+----+-------+------+------+
|  1 | tom   |   20 | nan  |
|  2 | jerry |   23 | nv   |
|  3 | zsl   |   18 | nan  |
|  4 | sean  |   25 | nv   |
+----+-------+------+------+
4 rows in set (0.00 sec)

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

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

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

mysql> desc zsltable;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id    | int(10)      | NO   |     | NULL    |       |
| name  | varchar(100) | NO   |     | NULL    |       |
| age   | tinyint(4)   | YES  |     | NULL    |       |
| sex   | varchar(4)   | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

3、DCL操作

3.1 创建授权grant

权限类型(priv_type)

指定要操作的对象db_name.table_name

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];

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

//授权lsz用户在数据库本机上登录访问所有数据库
mysql> GRANT ALL ON *.* TO 'lsz'@'localhost' IDENTIFIED BY 'Passwd123!';
Query OK, 0 rows affected, 1 warning (0.00 sec)

//也可表示为：
mysql> GRANT ALL ON *.* TO 'lsz'@'127.0.0.1' IDENTIFIED BY 'Passwd123!';
Query OK, 0 rows affected, 1 warning (0.00 sec)

//授权lsz用户在192.168.111.135上远程登录访问hzz数据库
mysql> GRANT ALL ON lsz.* TO 'lsz'@'192.168.111.135' IDENTIFIED BY 'Passwd123!';
Query OK, 0 rows affected, 1 warning (0.00 sec)

//授权lsz用户在所有位置上远程登录访问lsz数据库
mysql> GRANT ALL ON lsz.* TO 'lsz'@'%' IDENTIFIED BY 'Passwd123!';
Query OK, 0 rows affected, 1 warning (0.00 sec)

//刷新授权表
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

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

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 'lsz'@'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;

实战案例

1.搭建mysql服务

[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 ~]# dnf -y install mysql-community-server mysql-community-client mysql-community-common mysql-community-devel  --nogpgcheck
[root@localhost ~]# systemctl enable --now mysqld

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)

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

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

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 |
+----+-------------+------+

mysql> insert into student (id,name,age) values(1,'tom',20),(2,'jerry',23),(3,'wangqing',25),(4,'seann',28),(5,'zhangsan',26),(6,'zhangsan',20),(7,'lisi',null),(8,'chenshuo',10),(9,'wangwu',3),(10,'qiuyyi',15),(11,'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 | seann       |   28 |
|  5 | zhangsan    |   26 |
|  6 | zhangsan    |   20 |
|  7 | lisi        | NULL |
|  8 | chenshuo    |   10 |
|  9 | wangwu      |    3 |
| 10 | qiuyyi      |   15 |
| 11 | qiuxiaotian |   20 |
+----+-------------+------+
11 rows in set (0.01 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 order by age desc;
+----+-------------+------+
| id | name        | age  |
+----+-------------+------+
|  7 | lisi        |   50 |
|  4 | seann       |   28 |
|  5 | zhangsan    |   26 |
|  3 | wangqing    |   25 |
|  2 | jerry       |   23 |
|  1 | tom         |   20 |
|  6 | zhangsan    |   20 |
| 11 | qiuxiaotian |   20 |
| 10 | qiuyyi      |   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  limit 2,3;
+----+-------------+------+
| id | name        | age  |
+----+-------------+------+
| 10 | qiuyyi      |   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 limit 4;
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  7 | lisi     |   50 |
|  4 | seann    |   28 |
|  5 | zhangsan |   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 = 'zhangsan' ;
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  5 | zhangsan |   26 |
|  6 | zhangsan |   20 |
+----+----------+------+
2 rows in set (0.00 sec)

10.查询student表中名字叫zhangshan且年龄大于20岁的记录

mysql> select * from student where name = 'zhangsan' and age >20;
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  5 | zhangsan |   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 | seann    |   28 |
|  5 | zhangsan |   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>  delete from student where name ='zhangsan'and age<=20;
Query OK, 1 row affected (0.00 sec)

mysql> select * from student where name = 'zhangsan' and age<=20;
Empty set (0.00 sec)