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一、SQL结构化语言介绍
数据查询语言DQL：其语句称为“数据检索语言”，用以从库中获取数据，确定数据怎样在应用程序给出，保留select是dql（也是所有sql）用的最多的动词
数据操作语言DML:其语句包括动词insert，update和delete，分别用于添加，修改和删除表中的行，也称为动词查询语言
数据控制语言DCL：他的语句通过grant或者revoke获得许可，确定单个用户和用户组对数据库对象的访问，某些rdbms可用grant或者revoke控制对表单个列的访问。
数据定义语言DDL：其语句包括动词create和drop，在数据库创建新表或者删除表，为表加入索引等，DDL包括许多人数据库目录中获得数据有关的保留字，他也是动作查询的一部分。
二、数据定义语言DDL
1.系统数据库的介绍
information_schema 虚拟库，主要存储了系统中的一些数据库对象的信息，例如用户 表信息、列信息、权限信息、字符信息等
performance_schema 主要存储数据库服务器的性能参数
mysql 授权库，主要存储系统用户的权限信息
sys 主要存储数据库服务器的性能参数（目标是把 performance_schema的把复杂度降低）
2.创建数据库：DDL
（1）命令行创建数据库
语法;mysql -u用户 -p密码 -e “create database 数据库名 default charset ‘utf8’ ”
[root@localhost ~]# mysql -uroot -p123 -e "create database db2 default charset 'utf8'"（2）在mysql里面创建数据库
语法：create database 数据库名 指定字符集 ；
mysql> create database db3 default charset 'utf8';
Query OK, 1 row affected (0.00 sec)数据库命名规则：
区分大小写
唯一性
不能使用关键字 create select
不能单独使用数字
（3）查看所有数据库
语法：show databases；
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| db1 |
| db2 |
| db3 |
| mysql |
| performance_schema |
| school |
| sys |
+--------------------+
8 rows in set (0.00 sec)（4）查看创建库的信息
语法：show create database 库名；
mysql> show create database db2;
+----------+--------------------------------------------------------------+
| Database | Create Database |
+----------+--------------------------------------------------------------+
| db2 | CREATE DATABASE `db2` /*!40100 DEFAULT CHARACTER SET utf8 */ |
+----------+--------------------------------------------------------------+
1 row in set (0.00 sec)（5）查看当前库（路径）
语法：select database（）；
mysql> select database();
+------------+
| database() |
+------------+
| db2 |
+------------+
1 row in set (0.00 sec)（6）切换数据库
语法:use 数据库名；
mysql> use db2
Database changedmysql> show tables;
Empty set (0.00 sec)（7）删除数据库
语法：drop database 库名；
mysql> drop database db2;
Query OK, 0 rows affected (0.01 sec)3.表的DDL操作
（1）在命令行创建表
语法：mysql -u用户 -p密码 -e “use 库名；create table 表名 （字段 数据类型 约束条件）”
[root@localhost ~]# mysql -uroot -p123 -e"use db3;create table t1(name varchar(30),age int)"
mysql: [Warning] Using a password on the command line interface can be insecure.（2）在数据库中创建表
语法：create table 表名(字段名称 数据类型 约束条件)
mysql> create table t2(-> id int primary key auto_increment not null,-> age int,-> name varchar(40)-> );
Query OK, 0 rows affected (0.00 sec)
（3）查看表结构
语法：desc 表名；
mysql> desc t2;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| age | int(11) | YES | | NULL | |
| name | varchar(40) | YES | | NULL | |
+-------+-------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)（4）显示数据的详细信息
语法：show create 表名；
show table status like '表名'；
mysql> show create table t2;
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t2 | CREATE TABLE `t2` (`id` int(11) NOT NULL AUTO_INCREMENT,`age` int(11) DEFAULT NULL,`name` varchar(40) DEFAULT NULL,PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)mysql> show table status like 't2' \G
*************************** 1. row ***************************Name: t2Engine: InnoDBVersion: 10Row_format: DynamicRows: 0Avg_row_length: 0Data_length: 16384
Max_data_length: 0Index_length: 0Data_free: 0Auto_increment: 1Create_time: 2023-09-28 08:33:56Update_time: NULLCheck_time: NULLCollation: utf8_general_ciChecksum: NULLCreate_options: Comment:
1 row in set (0.00 sec)（5）添加字段
语法：alter table 表名 add 字段名称 字段类型 约束条件；
mysql> alter table t2 add math int not null;#新字段 数据类型 约束条件
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0（6）修改数据类型
语法：alter table 表名 modify 字段名 新的数据类型 新的约束条件；
mysql> alter table t2 modify math varchar(20) null; #将数据类型改为varchar，约束条件改变
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0（7）修改字段名（列）和数据类型
语法：alter table 表名 change 旧字段名 新字段名 新的数据类型 约束条件；
mysql> alter table t2 change math chinese int null; #将math改名为Chinese，int ，null
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0（8）删除字段名（列）
语法：alter table 表名 drop 字段名；
mysql> alter table t2 drop chinese;
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0（9）删除表
语法：drop table 表名；
mysql> drop table t2;
Query OK, 0 rows affected (0.00 sec)
三、数据操作语言DML
1.插入数据
语法：insert into 表名（字段1...字段n）values（值1....值n）
mysql> insert into employee values (1,'qiancheng','man','20180314','hr','talk',7000,501,102);
Query OK, 1 row affected (0.00 sec)mysql> insert into employee(id,name,hire_date,post,salary) values (50,'zxvb','20190423','hr',8000);
Query OK, 1 row affected (0.00 sec)mysql> insert into employee(id,name,salary) values(51,'ab',6500), (52,'cd',7600), (53,'ef',8900);
Query OK, 3 rows affected (0.01 sec)
Records: 3 Duplicates: 0 Warnings: 02.更新数据update
语法：update 表名 set 字段1=值1，字段2=值2 where 条件；
mysql> update employee6 set emp_name='ab';
Query OK, 6 rows affected (0.00 sec)
Rows matched: 6 Changed: 6 Warnings: 0mysql> select * from employee6;
+--------+----------+------+---------+
| emp_id | emp_name | age | dept_id |
+--------+----------+------+---------+
| 1 | ab | 19 | 200 |
| 2 | ab | 26 | 201 |
| 3 | ab | 30 | 201 |
| 4 | ab | 24 | 202 |
| 5 | ab | 40 | 200 |
| 6 | ab | 28 | 204 |
+--------+----------+------+---------+
6 rows in set (0.00 sec)mysql> update employee6 set emp_name='cd' where emp_id=3;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0mysql> select * from employee6;
+--------+----------+------+---------+
| emp_id | emp_name | age | dept_id |
+--------+----------+------+---------+
| 1 | ab | 19 | 200 |
| 2 | ab | 26 | 201 |
| 3 | cd | 30 | 201 |
| 4 | ab | 24 | 202 |
| 5 | ab | 40 | 200 |
| 6 | ab | 28 | 204 |
+--------+----------+------+---------+
6 rows in set (0.00 sec)3.删除数据delete
语法：delete from 表名 where 条件；
mysql> select * from employee6;
+--------+----------+------+---------+
| emp_id | emp_name | age | dept_id |
+--------+----------+------+---------+
| 1 | ab | 19 | 200 |
| 2 | ab | 26 | 201 |
| 4 | ab | 24 | 202 |
| 5 | ab | 40 | 200 |
| 6 | ab | 28 | 204 |
+--------+----------+------+---------+
5 rows in set (0.00 sec)mysql> delete from employee6;
Query OK, 5 rows affected (0.01 sec)mysql> select * from employee6;
Empty set (0.00 sec)mysql> desc employee6;
+----------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+----------------+
| emp_id | int(11) | NO | PRI | NULL | auto_increment |
| emp_name | varchar(50) | YES | | NULL | |
| age | int(11) | YES | | NULL | |
| dept_id | int(11) | YES | | NULL | |
+----------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec）四、数据查询语言DQL
1.单表查询
（1).基础查询
a.查询所有信息
语法 ：select * from 表名；
mysql> select * from employee;
+----+----------+-------+------------+------------+-----------------+----------+--------+--------+
| id | name | sex | hire_date | post | job_description | salary | office | dep_id |
+----+----------+-------+------------+------------+-----------------+----------+--------+--------+
| 20 | tom | man | 2017-09-15 | instructor | teach | 8000.00 | 501 | 100 |
| 21 | alince | woman | 2013-04-28 | instructor | teach | 5500.00 | 501 | 100 |
| 22 | robin | man | 2020-09-18 | instructor | teach | 7200.00 | 501 | 100 |
| 23 | zhuzhu | man | 2016-12-09 | hr | hrcc | 6000.00 | 502 | 101 |
| 24 | gougou | woman | 2015-04-27 | hr | NULL | 6000.00 | 502 | 101 |
| 30 | maomao | man | 2019-08-12 | sale | talk | 20000.00 | 503 | 102 |
| 31 | yiyi | man | 2015-06-17 | talk | NULL | 8000.00 | NULL | NULL |
| 40 | harry | woman | 2018-02-05 | hr | hrcc | 6900.00 | 502 | 102 |
| 41 | tianyuan | man | 2018-02-05 | null | salecc | 9700.00 | 501 | 102 |
| 42 | xiaoyi | man | 2018-02-05 | null | salecc | 5700.00 | 501 | 102 |
+----+----------+-------+------------+------------+-----------------+----------+--------+--------+
10 rows in set (0.00 sec)
b.去除重复记录
语法：select distinct 字段 from 表名；
mysql> select distinct office from employee;
+--------+
| office |
+--------+
| 501 |
| 502 |
| 503 |
| NULL |
+--------+
4 rows in set (0.00 sec)（2）.条件查询
语法： select 字段 from 表名 where 条件列表
#单条件查询
mysql> select name,salary from employee where salary = 8000
;
+------+---------+
| name | salary |
+------+---------+
| tom | 8000.00 |
| yiyi | 8000.00 |
+------+---------+
2 rows in set (0.00 sec)
#多条件查询
mysql> select name,salary from employee where salary between 4000 and 20000;
+----------+----------+
| name | salary |
+----------+----------+
| tom | 8000.00 |
| alince | 5500.00 |
| robin | 7200.00 |
| zhuzhu | 6000.00 |
| gougou | 6000.00 |
| maomao | 20000.00 |
| yiyi | 8000.00 |
| harry | 6900.00 |
| tianyuan | 9700.00 |
| xiaoyi | 5700.00 |
+----------+----------+
10 rows in set (0.00 sec)
mysql> select name,salary from employee where salary=4000 or salary=6000;
+--------+---------+
| name | salary |
+--------+---------+
| zhuzhu | 6000.00 |
| gougou | 6000.00 |
+--------+---------+
2 rows in set (0.00 sec)
关键字is
#查询employee中office为空的人
mysql> select name,office from employee where office is null;
+------+--------+
| name | office |
+------+--------+
| yiyi | NULL |
+------+--------+
1 row in set (0.00 sec)#查询employee表中office不为空的人mysql> select name,office from employee where office is notnull;
+----------+--------+
| name | office |
+----------+--------+
| tom | 501 |
| alince | 501 |
| robin | 501 |
| zhuzhu | 502 |
| gougou | 502 |
| maomao | 503 |
| harry | 502 |
| tianyuan | 501 |
| xiaoyi | 501 |
+----------+--------+
9 rows in set (0.00 sec)关键字in
#查询employee表中工资为4000,8000，20000的员工
mysql> select name,salary from employee where salary in (4000, 8000,20000);
+--------+----------+
| name | salary |
+--------+----------+
| tom | 8000.00 |
| maomao | 20000.00 |
| yiyi | 8000.00 |
+--------+----------+
3 rows in set (0.00 sec)
mysql> select name,salary from employee where salary in (4000,8000,20000);
+--------+----------+
| name | salary |
+--------+----------+
| tom | 8000.00 |
| maomao | 20000.00 |
| yiyi | 8000.00 |
+--------+----------+
3 rows in set (0.01 sec)（3）.排序查询
语法：select 字段 from 表名 order by 排序字段1，排序字段2
ASC：升序排列（默认）
DESC：降序排列
#按名字升序排列
mysql> select name from employee order by name;
+----------+
| name |
+----------+
| alince |
| gougou |
| harry |
| maomao |
| robin |
| tianyuan |
| tom |
| xiaoyi |
| yiyi |
| zhuzhu |
+----------+
10 rows in set (0.00 sec)#按名字倒叙排列
mysql> select name from employee order by name desc;
+----------+
| name |
+----------+
| zhuzhu |
| yiyi |
| xiaoyi |
| tom |
| tianyuan |
| robin |
| maomao |
| harry |
| gougou |
| alince |
+----------+
10 rows in set (0.00 sec)从第四行开始显示5行
mysql> select name from employee order by name desc limit 3, 5;
+----------+
| name |
+----------+
| tom |
| tianyuan |
| robin |
| maomao |
| harry |
+----------+
5 rows in set (0.00 sec)
#按多列排序，先按入职时间，再按工资
mysql> select * from employee order by hire_date,salary asc;
+----+----------+-------+------------+------------+-----------------+----------+--------+--------+
| id | name | sex | hire_date | post | job_description | salary | office | dep_id |
+----+----------+-------+------------+------------+-----------------+----------+--------+--------+
| 21 | alince | woman | 2013-04-28 | instructor | teach | 5500.00 | 501 | 100 |
| 24 | gougou | woman | 2015-04-27 | hr | NULL | 6000.00 | 502 | 101 |
| 31 | yiyi | man | 2015-06-17 | talk | NULL | 8000.00 | NULL | NULL |
| 23 | zhuzhu | man | 2016-12-09 | hr | hrcc | 6000.00 | 502 | 101 |
| 20 | tom | man | 2017-09-15 | instructor | teach | 8000.00 | 501 | 100 |
| 42 | xiaoyi | man | 2018-02-05 | null | salecc | 5700.00 | 501 | 102 |
| 40 | harry | woman | 2018-02-05 | hr | hrcc | 6900.00 | 502 | 102 |
| 41 | tianyuan | man | 2018-02-05 | null | salecc | 9700.00 | 501 | 102 |
| 30 | maomao | man | 2019-08-12 | sale | talk | 20000.00 | 503 | 102 |
| 22 | robin | man | 2020-09-18 | instructor | teach | 7200.00 | 501 | 100 |
+----+----------+-------+------------+------------+-----------------+----------+--------+--------+
10 rows in set (0.00 sec)
（4）分组查询
语法：select 字段,(group_concat(字段名)） from 表名 group by 字段名；
GROUP_CONCAT 函数用于将一个分组内的多行数据合并成一个字符串，并以指定的分隔符进行分隔。
mysql> select post from employee group by post;
+------------+
| post |
+------------+
| hr |
| instructor |
| null |
| sale |
| talk |
+------------+mysql> select post,group_concat(name) from employee group by post;
+------------+---------------------+
| post | group_concat(name) |
+------------+---------------------+
| hr | zhuzhu,gougou,harry |
| instructor | tom,alince,robin |
| null | tianyuan,xiaoyi |
| sale | maomao |
| talk | yiyi |
+------------+---------------------+
5 rows in set (0.00 sec)mysql> select post,group_concat(id) from employee group by
post;
+------------+------------------+
| post | group_concat(id) |
+------------+------------------+
| hr | 23,24,40 |
| instructor | 20,21,22 |
| null | 41,42 |
| sale | 30 |
| talk | 31 |
+------------+------------------+
5 rows in set (0.00 sec)（5）模糊查询（通配符%）
mysql> select * from employee where salary like "%20%";
+----+--------+------+------------+------------+-----------------+----------+--------+--------+
| id | name | sex | hire_date | post | job_description | salary | office | dep_id |
+----+--------+------+------------+------------+-----------------+----------+--------+--------+
| 22 | robin | man | 2020-09-18 | instructor | teach | 7200.00 | 501 | 100 |
| 30 | maomao | man | 2019-08-12 | sale | talk | 20000.00 | 503 | 102 |
+----+--------+------+------------+------------+-----------------+----------+--------+--------+
2 rows in set (0.00 sec)（6）正则查询
mysql> select * from employee where salary regexp '72+';
+----+-------+------+------------+------------+-----------------+---------+--------+--------+
| id | name | sex | hire_date | post | job_description | salary | office | dep_id |
+----+-------+------+------------+------------+-----------------+---------+--------+--------+
| 22 | robin | man | 2020-09-18 | instructor | teach | 7200.00 | 501 | 100 |
+----+-------+------+------------+------------+-----------------+---------+--------+--------+
1 row in set (0.00 sec)mysql> select * from employee where name regexp '^xiao';
+----+--------+------+------------+------+-----------------+---------+--------+--------+
| id | name | sex | hire_date | post | job_description | salary | office | dep_id |
+----+--------+------+------------+------+-----------------+---------+--------+--------+
| 42 | xiaoyi | man | 2018-02-05 | null | salecc | 5700.00 | 501 | 102 |
+----+--------+------+------------+------+-----------------+---------+--------+--------+
1 row in set (0.00 sec)mysql> select * from employee where name regexp "yi$";
+----+--------+------+------------+------+-----------------+---------+--------+--------+
| id | name | sex | hire_date | post | job_description | salary | office | dep_id |
+----+--------+------+------------+------+-----------------+---------+--------+--------+
| 31 | yiyi | man | 2015-06-17 | talk | NULL | 8000.00 | NULL | NULL |
| 42 | xiaoyi | man | 2018-02-05 | null | salecc | 5700.00 | 501 | 102 |
+----+--------+------+------------+------+-----------------+---------+--------+--------+
2 rows in set (0.00 sec)mysql> select * from employee where name regexp "yi$";
+----+--------+------+------------+------+-----------------+---------+--------+--------+
| id | name | sex | hire_date | post | job_description | salary | office | dep_id |
+----+--------+------+------------+------+-----------------+---------+--------+--------+
| 31 | yiyi | man | 2015-06-17 | talk | NULL | 8000.00 | NULL | NULL |
| 42 | xiaoyi | man | 2018-02-05 | null | salecc | 5700.00 | 501 | 102 |
+----+--------+------+------------+------+-----------------+---------+--------+--------+
2 rows in set (0.00 sec)
2.多表查询
a) 内连接
只连接匹配的行
mysql> select employee6.emp_id,employee6.emp_name,employee6.age,department.dept_name from employee6,department where employee6.dept_id = department.dept_id;
+--------+----------+------+-----------+
| emp_id | emp_name | age | dept_name |
+--------+----------+------+-----------+
| 1 | tianyun | 19 | hr |
| 2 | tom | 26 | it |
| 3 | jack | 30 | it |
| 4 | alice | 24 | yunwei |
| 5 | robin | 40 | hr |
+--------+----------+------+-----------+
5 rows in set (0.00 sec)mysql> select a.emp_id,a.emp_name,a.age,b.dept_name from employee6 a,department b where a.dept_id=b.dept_id;
+--------+----------+------+-----------+
| emp_id | emp_name | age | dept_name |
+--------+----------+------+-----------+
| 1 | tianyun | 19 | hr |
| 2 | tom | 26 | it |
| 3 | jack | 30 | it |
| 4 | alice | 24 | yunwei |
| 5 | robin | 40 | hr |
+--------+----------+------+-----------+
5 rows in set (0.00 sec)mysql> select a.emp_id,a.emp_name,a.age,b.dept_name from employee6 a inner join department b on a.dept_id=b.dept_id;
+--------+----------+------+-----------+
| emp_id | emp_name | age | dept_name |
+--------+----------+------+-----------+
| 1 | tianyun | 19 | hr |
| 2 | tom | 26 | it |
| 3 | jack | 30 | it |
| 4 | alice | 24 | yunwei |
| 5 | robin | 40 | hr |
+--------+----------+------+-----------+
5 rows in set (0.00 sec)
b)外连接
外连接：（了解）
左连接： 会显示左边表内所有的值，不论在右边表内匹不匹配
右连接： 会显示右边表内所有的值，不论在左边表内匹不匹配
语法：SELECT 字段 ROM 表1 LEFT|RIGHT JOIN 表2 ON 表1.字段 = 表2.字段;
mysql> select emp_id,emp_name,age,dept_name from employee6left join department on employee6.dept_id = department.dep
t_id;
+--------+----------+------+-----------+
| emp_id | emp_name | age | dept_name |
+--------+----------+------+-----------+
| 1 | tianyun | 19 | hr |
| 5 | robin | 40 | hr |
| 2 | tom | 26 | it |
| 3 | jack | 30 | it |
| 4 | alice | 24 | yunwei |
| 6 | natasha | 28 | NULL |
+--------+----------+------+-----------+
6 rows in set (0.00 sec)mysql> select emp_id,emp_name,age,dept_name from employee6right join department on employee6.dept_id = department.de
pt_id;
+--------+----------+------+-----------+
| emp_id | emp_name | age | dept_name |
+--------+----------+------+-----------+
| 1 | tianyun | 19 | hr |
| 2 | tom | 26 | it |
| 3 | jack | 30 | it |
| 4 | alice | 24 | yunwei |
| 5 | robin | 40 | hr |
| NULL | NULL | NULL | fd |
+--------+----------+------+-----------+
6 rows in set (0.00 sec)c)全外连接
全外连接：（了解） 包含左、右两个表的全部行
mysql> select * from employee6 full join department;
+--------+----------+------+---------+---------+-----------+
| emp_id | emp_name | age | dept_id | dept_id | dept_name |
+--------+----------+------+---------+---------+-----------+
| 1 | tianyun | 19 | 200 | 200 | hr |
| 1 | tianyun | 19 | 200 | 201 | it |
| 1 | tianyun | 19 | 200 | 202 | yunwei |
| 1 | tianyun | 19 | 200 | 203 | fd |
| 2 | tom | 26 | 201 | 200 | hr |
| 2 | tom | 26 | 201 | 201 | it |
| 2 | tom | 26 | 201 | 202 | yunwei |
| 2 | tom | 26 | 201 | 203 | fd |
| 3 | jack | 30 | 201 | 200 | hr |
| 3 | jack | 30 | 201 | 201 | it |
| 3 | jack | 30 | 201 | 202 | yunwei |
| 3 | jack | 30 | 201 | 203 | fd |
| 4 | alice | 24 | 202 | 200 | hr |
| 4 | alice | 24 | 202 | 201 | it |
| 4 | alice | 24 | 202 | 202 | yunwei |
| 4 | alice | 24 | 202 | 203 | fd |
| 5 | robin | 40 | 200 | 200 | hr |
| 5 | robin | 40 | 200 | 201 | it |
| 5 | robin | 40 | 200 | 202 | yunwei |
| 5 | robin | 40 | 200 | 203 | fd |
| 6 | natasha | 28 | 204 | 200 | hr |
| 6 | natasha | 28 | 204 | 201 | it |
| 6 | natasha | 28 | 204 | 202 | yunwei |
| 6 | natasha | 28 | 204 | 203 | fd |
+--------+----------+------+---------+---------+-----------+
24 rows in set (0.00 sec)五、数据库控制语言DCL
1.用户管理
（1）创建用户
语法：create user '用户名'@'客户端ip地址' identified by '密码'；
mysql> create user 'cd'@'10.36.192.%' identified by '123';
Query OK, 0 rows affected (0.00 sec)（2）修改用户信息
语法：rename user '用户名'@'客户端来源ip地址' to '新用户名'@'客户端来源IP地址'
mysql> rename user 'cd'@'10.36.192.%' to 'ef'@'192.168.142.%';
Query OK, 0 rows affected (0.00 sec)（3）修改普通用户的密码
a)语法：set password for '用户名'@'ip地址'=password（'新密码'）；
b)语法：alter user '用户名'@'客户端来源IP地址' identified by '新密码'；
c)语法：update mysql.user set authentication_string=password('密码') where user='root' and host='localhost';
mysql> set password for 'ef'@'192.168.142.%'=password('111');
Query OK, 0 rows affected, 1 warning (0.00 sec)mysql> alter user 'ef'@'192.168.142.%' identified by '123';
Query OK, 0 rows affected (0.00 sec)（4）删除用户
语法：drop user '用户名'@'客户端来源ip地址'；
mysql> drop user 'ef'@'192.168.142.%';
Query OK, 0 rows affected (0.00 sec)2.权限管理
（1）.给普通用户授权并授权
语法：grant 权限 on 数据库.表 to '用户'@'客户端来源IP地址' identified by '密码';
mysql> grant all on *.* to 'ef'@'192.168.142.%' identified
by '123';
Query OK, 0 rows affected, 1 warning (0.00 sec)
（2）.取消普通用户的权限
语法：revoke 权限 on 数据库.表 from '用户'@'客户端来源IP地址
mysql> revoke all on *.* from 'cd'@'192.168.142.%';
Query OK, 0 rows affected (0.00 sec)
（3）.刷新权限
语法：flush privileges；
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)（4）.查看授权信息
a.查看授权语句
语法：show grants for '用户'@'客户端来源IP地址';
mysql> show grants for 'ef'@'192.168.142.%';
+-----------------------------------------------------+
| Grants for ef@192.168.142.% |
+-----------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'ef'@'192.168.142.%' |
+-----------------------------------------------------+
1 row in set (0.00 sec)
b.查看生效的授权信息
语法：select * from mysql.user where user='用户'\G
mysql> select * from mysql.user where user='ef'\G
*************************** 1. row ***************************Host: 192.168.142.%User: efSelect_priv: YInsert_priv: YUpdate_priv: YDelete_priv: YCreate_priv: YDrop_priv: YReload_priv: YShutdown_priv: YProcess_priv: YFile_priv: YGrant_priv: NReferences_priv: YIndex_priv: YAlter_priv: YShow_db_priv: YSuper_priv: YCreate_tmp_table_priv: YLock_tables_priv: YExecute_priv: YRepl_slave_priv: YRepl_client_priv: YCreate_view_priv: YShow_view_priv: YCreate_routine_priv: YAlter_routine_priv: YCreate_user_priv: YEvent_priv: YTrigger_priv: Y
Create_tablespace_priv: Yssl_type: ssl_cipher: x509_issuer: x509_subject: max_questions: 0max_updates: 0max_connections: 0max_user_connections: 0plugin: mysql_native_passwordauthentication_string: *23AE809DDACAF96AF0FD78ED04B6A265E05AA257password_expired: Npassword_last_changed: 2023-09-28 15:06:11password_lifetime: NULLaccount_locked: N
1 row in set (0.00 sec)