学习MySQL之初步管理一篇就够了！（SQL语句举例说明，大家看了都说好）

博主熬夜整理出来的MySQL之原理，操作，和如何对数据库当中的数据的增删改查，复制数据库和表，以及抽取数据，和在忘记数据库密码的时候，修改密码。

一：数据库

1.1数据库概述

• 数据库作用：数据持久化保存，高可靠，高可用，数据的快速提取。
• 数据库存储类型：关系型数据库 非关系型数据库。
  数据保存在内存
• 优点：存取速度快
• 缺点：数据不能永久保存

数据保存在文件

• 优点：数据永久保存
• 缺点：速度比内存操作慢，频繁的IO操作。2）查询数据不方便

数据保存在数据库

• 数据永久保存
• 使用SQL语句，查询方便效率高。
• 管理数据方便

1.2：非关系型数据库

1.21：非关系型数据库存储方式

• 键-值方式(key–value),以键为依据存储、删、改数据
• 列存储(Column-oriented), 将相关的数据存储在列族中
• 文档的方式，数据库由-系列数据项组成，每个数据项都
• 有名称与对应的值

1.22：非关系型数据库(统称NOSQL)：

• redis(内存数据库/缓存数据库)： K-V键值对 key-value 变量名-值
• memcache (内存数据库/缓存数据库) ：K-V键值对

1.23：非关系型数据库的优点：

• 数据库高并发读写的需求
• 对海量数据高效率存储与访问
• 数据库的高扩展性与高可用性的需求

二：MySQL

2.1：登录数据库

• 注意MySQL的初始密码为空，通过mysql -u root -p进入回车，输入两次新密码即可设置新密码。
• 登录数据库
• 格式：mysql -h主机地址 -u用户名 -p用户密码
• 注：u与root可以不加空格

[root@server3 ~]# mysql -u root -p123123
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: 5.7.20 Source distribution
Copyright (c) 2000, 2017, 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> 

修改密码

• 格式：mysqladmin -u用户名 -p旧密码 password 新密码

2.2：查看数据库

mysql> SHOW DATABASES;    #大小写皆可，分号不能忘
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0.01 sec)

2.4：查看数据库中的数据表信息

use 数据库名     #切换到库
show tables 查看库中的表

mysql> use mysql;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed

mysql> show tables;
+---------------------------+
| Tables_in_mysql           |
+---------------------------+
| columns_priv              |
| db                        |
……省略内容
| time_zone                 |
| time_zone_leap_second     |
| time_zone_name            |
| time_zone_transition      |
| time_zone_transition_type |
| user                      |
+---------------------------+
31 rows in set (0.00 sec)

Mysql数据库的数据文件都存放在/usr/local/mysql/data目录下，每个数据库对应一个子目录，用于储存数据表文件。每一个数据表对应为三个文件，后缀名分别为’’.frm “.myd” 和“.myi"。当然也有少数以opt、csm、csv、ibd结尾的。

3、显示数据表的结构

describe [数据库名.]表名
例如：
describe mysql.time_zone;
或者
先切换到mysql库，再显示表结构。

mysql> describe mysql.time_zone;
+------------------+------------------+------+-----+---------+----------------+
| Field            | Type             | Null | Key | Default | Extra          |
+------------------+------------------+------+-----+---------+----------------+
| Time_zone_id     | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| Use_leap_seconds | enum('Y','N')    | NO   |     | N       |                |
+------------------+------------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)

三、SQL语句

3.1、SQL语言分类

数据库目前标准的指令是SQL。SQL是Structured Querl Language的缩写，即结构化查询语言。它是1974年有Boyce和Chamberlin提出来的，1975-1979年，IBM公司研制的关系数据库管理系统原型System R实现了这种语言，经过多年的发展，SQL语言得到了广泛的应用.
1、SQL语言

• 是Structured Query Language的缩写，即结构化查询语言
• 是关系型数据库的标准语言
• 用于维护管理数据库,如数据查询、数据更新、访问控制、对象管理等功能
  2、SQL分类
• DDL:数据定义语言
• DML:数据操纵语言
• DQL:数据查询语言
• DCL:数据控制语言

3.2、DDL语句

• DDL语句用于创建数据库对象，如库、表、索引等

1、使用DDL语句新建库、表
创建数据库

mysql> create database student;
Query OK, 1 row affected (0.01 sec)

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| student            |    #已经创建成功
| sys                |
+--------------------+
5 rows in set (0.00 sec)

mysql> use student;
Database changed
mysql> show tables;
Empty set (0.00 sec)

刚创建的数据库是空的，其中不包含任何表，在/usr/local/mysql/data目录下会自动生成一个与新建的库名相同的空文件。

创建数据表

CREATE TABLE 表名（字段定义...）

create table 表名（字段01名称 字段01类型 字段01约束，字段02名 字段02类型 字段02约束）存储引擎 字符集

【多个字段用，隔开】

字段01名称：属性名称，自定义

字段01类型：

• int （5） 整型 00000-99999
• double 浮点型
• decimal（5,2） 有效数字是5位，小数点后面保留2位100.00 088.45
• fioat 单精度浮点 4字节
• varchar（50） 可变长度字符串
• char（10） 固定长度字符串

字段01约束：

1、主键 PK primary key
2、唯一约束 UK unique key
3、外键约束 FK foreign key
4、非空约束 NN not null
5、检查约束 CK check
6、默认值约束 default

存数引擎：myisam innodb

字符集：UTF-8

mysql> create table info (id int(3) not null primary key,name char(10) not null,address varchar(50) default 'nj');
Query OK, 0 rows affected (0.02 sec)

mysql> show tables;
+-------------------+
| Tables_in_student |
+-------------------+
| info              |
+-------------------+
1 row in set (0.00 sec)
#查看表结构
mysql> describe info;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id      | int(3)      | NO   | PRI | NULL    |       |
| name    | char(10)    | NO   |     | NULL    |       |
| address | varchar(50) | YES  |     | nj      |       |
+---------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

删除指定的数据库：DROP DATABASE 数据库名

mysql> create database tom;
Query OK, 1 row affected (0.01 sec)

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

mysql> drop database tom;
Query OK, 0 rows affected (0.02 sec)

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| student            |  #tom已删除
| sys                |
+--------------------+
5 rows in set (0.00 sec)

3.2：管理表中的数据

DML语句用于对表中的数据进行管理

包括的操作

• INSERT:插入新数据
• UPDATE：更新原有数据
• DELETE：删除不不需要的数据

3.3：向数据表中插入新的数据记录（DML）

#第一种插入记录的方法：
insert into info (id,name,address) values (2,'lisi','上海'),(3,'wangwu','北京');
#第二种插入记录方式：
insert into info values (4,'yiyi','北京'); 

mysql> describe info;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id      | int(3)      | NO   | PRI | NULL    |       |
| name    | char(10)    | NO   |     | NULL    |       |
| address | varchar(50) | YES  |     | nj      |       |
+---------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

mysql> insert into info (id,name,address) values (2,'lisi','上海'),(3,'tom','杭州');
Query OK, 2 rows affected (0.01 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from info;
+----+------+---------+
| id | name | address |
+----+------+---------+
|  2 | lisi | 上海    |
|  3 | tom  | 杭州    |
+----+------+---------+
2 rows in set (0.00 sec)

#第二种方法

mysql> insert into info values (1,'潘玉彬','广州');
Query OK, 1 row affected (0.01 sec)

mysql> select * from info;
+----+-----------+---------+
| id | name      | address |
+----+-----------+---------+
|  1 | 潘玉彬     | 广州    |
|  2 | lisi      | 上海    |
|  3 | tom       | 杭州    |
+----+-----------+---------+
3 rows in set (0.00 sec)

mysql> show tables;
+-------------------+
| Tables_in_student |
+-------------------+
| info              |
| tom               |
+-------------------+
2 rows in set (0.00 sec)

mysql> describe tom;
+---------+--------------+------+-----+---------+----------------+
| Field   | Type         | Null | Key | Default | Extra          |
+---------+--------------+------+-----+---------+----------------+
| id      | int(3)       | NO   | PRI | NULL    | auto_increment |
| name    | varchar(10)  | NO   |     | NULL    |                |
| score   | decimal(5,2) | YES  |     | NULL    |                |
| address | varchar(50)  | YES  |     | 未知    |                |
+---------+--------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
mysql> insert into tom (id,name,score,address) values (1,'pyb',90.2,'hangzhou');
mysql> select * from tom;
+----+------+-------+----------+
| id | name | score | address  |
+----+------+-------+----------+
|  1 | pyb  | 90.20 | hangzhou |
+----+------+-------+----------+

这边不加字段名称也可直接添加字段的值（默认是所有字段）
mysql> insert into tom values (2,'lisi',88,'shanghai');
mysql> select * from tom;
+----+------+-------+----------+
| id | name | score | address  |
+----+------+-------+----------+
|  1 | pyb  | 90.20 | hangzhou |
|  2 | lisi | 88.00 | shanghai |
+----+------+-------+----------+
2 rows in set (0.00 sec)

#default定义未知
mysql> insert into tom (name,score,address) values ('luoli',77,'shanxi'),('meimei',55,default);
Query OK, 2 rows affected (0.01 sec)
Records: 2  Duplicates: 0  Warnings: 0
mysql> select * from tom;
+----+--------+-------+----------+
| id | name   | score | address  |
+----+--------+-------+----------+
|  1 | pyb    | 90.20 | hangzhou |
|  2 | lisi   | 88.00 | shanghai |
|  3 | luoli  | 77.00 | shanxi   |
|  4 | meimei | 55.00 | 未知     |
+----+--------+-------+----------+
mysql> insert into tom values (5,'wudi',75,'suzhou');
Query OK, 1 row affected (0.01 sec)

mysql> select * from tom;
+----+--------+-------+----------+
| id | name   | score | address  |
+----+--------+-------+----------+
|  1 | pyb    | 90.20 | hangzhou |
|  2 | lisi   | 88.00 | shanghai |
|  3 | luoli  | 77.00 | shanxi   |
|  4 | meimei | 55.00 | 未知     |
|  5 | wudi   | 75.00 | suzhou   |
+----+--------+-------+----------+
5 rows in set (0.00 sec)

#筛选大于75的信息
mysql> select * from tom where score > 75;
+----+-------+-------+----------+
| id | name  | score | address  |
+----+-------+-------+----------+
|  1 | pyb   | 90.20 | hangzhou |
|  2 | lisi  | 88.00 | shanghai |
|  3 | luoli | 77.00 | shanxi   |
+----+-------+-------+----------+
3 rows in set (0.00 sec)

#将tom表中大于80的数据，放入新建的jerry表
mysql> create table jerry as select * from tom where score > 80;
Query OK, 2 rows affected (0.08 sec)
Records: 2  Duplicates: 0  Warnings: 0
mysql> select * from jerry;
+----+------+-------+----------+
| id | name | score | address  |
+----+------+-------+----------+
|  1 | pyb  | 90.20 | hangzhou |
|  2 | lisi | 88.00 | shanghai |
+----+------+-------+----------+
2 rows in set (0.00 sec)
#查看jerry表数据   已经克隆过来了
mysql> show tables;
+-------------------+
| Tables_in_student |
+-------------------+
| jerry             |
| tom               |
+-------------------+
2 rows in set (0.00 sec)

3.4：修改、更新数据表中的数据记录

UPDATE 表名 SET 字段名1=值1[,字段名2=值2] WHERE条件表达式
#将tom表中lisi的分数替换为55
mysql> update tom set score=55 where name='lisi';
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0
mysql> select * from tom;
+----+--------+-------+----------+
| id | name   | score | address  |
+----+--------+-------+----------+
|  1 | pyb    | 90.20 | hangzhou |
|  2 | lisi   | 55.00 | shanghai |
|  3 | luoli  | 77.00 | shanxi   |
|  4 | meimei | 55.00 | 未知     |
|  5 | wudi   | 75.00 | suzhou   |
+----+--------+-------+----------+
5 rows in set (0.00 sec)

• 通过修改数据库的方式实现修改数据库管理员密码

mysql> use mysql
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Database changed
mysql> show tables;
+---------------------------+
| Tables_in_mysql           |
+---------------------------+
| columns_priv              |
| db                        |
| engine_cost               |
……
| time_zone_transition_type |
| user                      |
+---------------------------+
31 rows in set (0.00 sec)
mysql> select user from user;
+---------------+
| user          |
+---------------+
| bbsuser       |
| root          |
| bbsuser       |
| mysql.session |
| mysql.sys     |
| root          |
| root          |
+---------------+
7 rows in set (0.06 sec)

3.5：设置用户权限的命令

• 若是用户已存在，则会更改用户密码
• 若是用户不存在，则是新建用户
• GRANT 权限列表 ON 数据库名.表名 TO 用户名@来源地址 [IDENTIFIED BY ‘密码′ ]

#创建用户

mysql> grant all privileges on *.* to 'liu'@'loaclhost' identified by 'abc123';
Query OK, 0 rows affected, 1 warning (0.06 sec)
#mysql数据库的内置库提取到内存里
mysql> flush privileges;
Query OK, 0 rows affected (0.02 sec)
#登录用户成功
mysql> select user from user;
+---------------+
| user          |
+---------------+
| bbsuser       |
| root          |
| liu           |
| bbsuser       |
| mysql.session |
| mysql.sys     |
| root          |
| root          |
+---------------+
8 rows in set (0.00 sec)
mysql> grant all privileges on *.* to 'liu'@'localhost' identified by '123123';
Query OK, 0 rows affected, 1 warning (0.00 sec)
#mysql数据库的内置库提取到内存里
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)
#登录用户成功
[root@server3 ~]# mysql -u liu -p123123
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 25
Server version: 5.7.20 Source distribution
Copyright (c) 2000, 2017, 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.

3.6：在数据库表中删除指定的数据记录

DELETE FPOM 表名 WHERE 条件表达式

mysql> select * from tom;
+----+--------+-------+----------+
| id | name   | score | address  |
+----+--------+-------+----------+
|  1 | pyb    | 55.00 | hangzhou |
|  2 | lisi   | 55.00 | shanghai |
|  3 | luoli  | 77.00 | shanxi   |
|  4 | meimei | 55.00 | 未知     |
|  5 | wudi   | 75.00 | suzhou   |
+----+--------+-------+----------+
5 rows in set (0.00 sec)

mysql> delete from tom where score <=60;
Query OK, 3 rows affected (0.01 sec)

mysql> select * from tom;
+----+-------+-------+---------+
| id | name  | score | address |
+----+-------+-------+---------+
|  3 | luoli | 77.00 | shanxi  |
|  5 | wudi  | 75.00 | suzhou  |
+----+-------+-------+---------+
2 rows in set (0.00 sec)

#真谨慎操作，删除全部内容
mysql> delete from tom;
Query OK, 0 rows affected (0.00 sec）
mysql> select * from tom;
Empty set (0.00 sec)

3.7：DQL是数据查询语句，只有SELECT

用于从数据表中查找符合条件的数据记录
查询时不指定条件

#SELECT 字段名1，字段名2....FROM表名 WHERE 条件表达式
mysql> select name,score from jerry where address='hangzhou';
+------+-------+
| name | score |
+------+-------+
| pyb  | 90.20 |
+------+-------+
1 row in set (0.00 sec)

3.8：清空表

• DELETE FROM tablename
• TRUNCATE TABLE tablename
• truncate与drop区别

drop是删除表 truncate 是情况里面的数据

mysql> truncate table jerry;
Query OK, 0 rows affected (0.01 sec)
mysql> select * from jerry;
Empty set (0.00 sec)
mysql> 

3.9：临时表

临时建立的表，用于保存一些临时数据，不会长期存在

mysql> create temporary table cdc (id int(3) not null auto_increment,name varchar(10) not null,hobby varchar(10) not null,primary key(id))engine=innodb default charset=utf8;
Query OK, 0 rows affected (0.00 sec)
mysql> describe cdc;
+-------+-------------+------+-----+---------+----------------+
| Field | Type        | Null | Key | Default | Extra          |
+-------+-------------+------+-----+---------+----------------+
| id    | int(3)      | NO   | PRI | NULL    | auto_increment |
| name  | varchar(10) | NO   |     | NULL    |                |
| hobby | varchar(10) | NO   |     | NULL    |                |
+-------+-------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
mysql> insert into cdc (name,hobby) values ('boy','dog');
Query OK, 1 row affected (0.00 sec)

mysql> select * from cdc;
+----+------+-------+
| id | name | hobby |
+----+------+-------+
|  1 | boy  | dog   |
+----+------+-------+
1 row in set (0.00 sec)
mysql> show tables;
+-------------------+
| Tables_in_student |
+-------------------+
| info              |
| jerry             |
| tom               |
+-------------------+
3 rows in set (0.00 sec)
#不在硬盘上，在内存上

测试临时表断开连接会自动删除

[root@server3 ~]# mysql -u liu -p123321
……省略
mysql> use cdc;
ERROR 1049 (42000): Unknown database 'cdc'
mysql> select * from cdc;
ERROR 1046 (3D000): No database selected

3.10：临时表

3.11：create方法

#查看hei表信息结构
mysql> select * from hei;
+----+--------+-------+-----------+
| id | name   | score | address   |
+----+--------+-------+-----------+
|  1 | lisi   | 44.50 | doongjing |
|  2 | wangwu | 77.00 | xiamen    |
+----+--------+-------+-----------+
2 rows in set (0.00 sec)
#查询的语句生成一张新表hh
mysql> create table hh as select * from hei;
#已经生成
mysql> select * from xiao;
+----+------+-------+
| id | name | hobby |
+----+------+-------+
|  1 | q    | run   |
|  2 | x    | fly   |
+----+------+-------+
2 rows in set (0.00 sec)

mysql> show tables;
+-------------------+
| Tables_in_student |
+-------------------+
| hai               |
| info              |
| jerry             |
| tom               |
| xiao              |
+-------------------+
5 rows in set (0.00 sec)

mysql> select xiao;
ERROR 1054 (42S22): Unknown column 'xiao' in 'field list'
mysql> select * from xiao;
+----+------+-------+
| id | name | hobby |
+----+------+-------+
|  1 | q    | run   |
|  2 | x    | fly   |
+----+------+-------+
2 rows in set (0.00 sec)
mysql> create table hai as select * from xiao;
mysql> select * from hai;
+----+------+-------+
| id | name | hobby |
+----+------+-------+
|  1 | q    | run   |
|  2 | x    | fly   |
+----+------+-------+
2 rows in set (0.00 sec)

#查看hai表结构  可以看出跟xiao表一样
mysql> desc hai;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(3)      | NO   |     | 0       |       |
| name  | varchar(10) | NO   |     | NULL    |       |
| hobby | varchar(10) | NO   |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

克隆也可分为两部分：第一步复制结构生成表 （结构没有数据）第二步 导入数据

3.12：LIKE方法

从hei表完整复制结构生成gg表

mysql> create table jerry like tom;
Query OK, 0 rows affected (0.00 sec)
#查看所有表
mysql> show tables;
+---------------+
| Tables_in_mei |
+---------------+
| jerry         |
| tom           |
+---------------+
2 rows in set (0.00 sec)
#新表jerry是没有数据的 
mysql> select * from jerry;
Empty set (0.00 sec)

• 先查看hei表完整结构，根据结构创建名字不同结构相同的表gg，再导入数据

四：数据库用户授权

DCL语句设置用户权限（用户不存在时；则会新建用户）

• 若用户已存在，则更改用户密码
• 若用户不存在，则新建用户

GRANT 权限列表 ON 数据库名，表名 TO 用户名@来源地址 [IDENTILED BY '密码’]

GRANT 权限列表 ON 数据库名，表名 TO 用户名@来源地址 [IDENTILED BY '密码’]
1
# *.*：所有数据库所有表 
mysql> grant all on *.* to 'tom'@'locahost' identified by 'abc123'; 
Query OK, 0 rows affected, 1 warning (0.00 sec)

##mysql数据库的内置库提取到内存里。
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

#all privileges：所有权限，%：所有终端'
mysql> grant all privileges on *.* to 'root'@'%' identified by 'abc123';
Query OK, 0 rows affected, 1 warning (0.00 sec)

4.1：查看用户的权限

SHOW GRANTS FOR 用户名@来源地址

查看用户权限

mysql> show grants for 'root'@'%';
+-------------------------------------------+
| Grants for root@%                         |
+-------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'root'@'%' | # 拥有所有权限
+-------------------------------------------+
1 row in set (0.00 sec)

查看数据库有哪些用户

mysql> select user from mysql.user;
+---------------+
| user          |
+---------------+
| bbsuser       |
| root          |
| liu           |
| tom           |
| bbsuser       |
| liu           |
| mysql.session |
| mysql.sys     |
| root          |
| root          |
+---------------+
10 rows in set (0.00 sec)

4.2：撤销用户权限的命令

REVOKE 权限列表 ON 数据库名.表名 FROM 用户名@来源地址

mysql> revoke all privileges on *.* from 'root'@'%';
Query OK, 0 rows affected (0.00 sec)

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

五：密码如果是遗忘密码怎么修改？

[root@server3 ~]# vi /etc/my.cnf
[mysqld]
user = mysql
basedir = /usr/local/mysql
datadir = /usr/local/mysql/data
port = 3306
character_set_server=utf8
pid-file = /usr/local/mysql/mysqld.pid
socket = /usr/local/mysql/mysql.sock
server-id = 1
skip-grant-tables                                       #添加此行，跳过表的加载
skip-grant-tables
[root@server3 ~]# systemctl restart mysqld.service      #重启服务
[root@server3 ~]# netstat -anpt | grep 3306
tcp6       0      0 :::3306                 :::*                    LISTEN      1282/mysqld     
[root@server3 ~]# mysql -u root -p
Enter password:                                         #回车直接登录
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.7.20 Source distribution
Copyright (c) 2000, 2017, 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账户也同样
[root@server3 ~]# mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.7.20 Source distribution
Copyright (c) 2000, 2017, 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@server3 ~]# mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.7.20 Source distribution
Coperight (c) 2000, 2017, 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> update mysql.user set authentication_string=password('123321') where user='liu';
Query OK, 2 rows affected, 1 warning (0.00 sec)
Rows matched: 2  Changed: 2  Warnings: 1
mysql> quit
Bye
[root@server3 ~]# vi /etc/my.cnf
#取消注释
[root@server3 ~]# systemctl restart mysqld.service 
[root@server3 ~]# mysql -u liu -p123321
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: 5.7.20 Source distribution
Copyright (c) 2000, 2017, 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> 

• 下面的文件为MySQL中储存用户和密码以及其他信息的地方，替换当中的字段，重启服务就可以使用新密码登录

#截取一段做分析
mysql> select * from user\G;
*************************** 1. row ***************************
                  Host: localhost
                  User: root           #用户名
           Select_priv: Y
           Insert_priv: Y
           Update_priv: Y
           Delete_priv: Y
           Create_priv: Y
             Drop_priv: Y
           Reload_priv: Y
         Shutdown_priv: Y
          Process_priv: Y
             File_priv: Y
            Grant_priv: Y
       References_priv: Y
            Index_priv: Y
            Alter_priv: Y
          Show_db_priv: Y
            Super_priv: Y
 Create_tmp_table_priv: Y
      Lock_tables_priv: Y
          Execute_priv: Y
       Repl_slave_priv: Y
      Repl_client_priv: Y
      Create_view_priv: Y
        Show_view_priv: Y
   Create_routine_priv: Y
    Alter_routine_priv: Y
      Create_user_priv: Y
            Event_priv: Y
          Trigger_priv: Y
Create_tablespace_priv: Y
              ssl_type: 
            ssl_cipher: 
           x509_issuer: 
          x509_subject: 
         max_questions: 0
           max_updates: 0
       max_connections: 0
  max_user_connections: 0
                plugin: mysql_native_password
 authentication_string: *E56A114692FE0DE073F9A1DD68A00EEB9703F3F1    #密码字段
      password_expired: N
 password_last_changed: 2020-10-16 16:05:55
     password_lifetime: NULL
        account_locked: N

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