一 host中的含义

/usr/local/mysql/bin/mysql -p'LXYlxy2:024.#8u}' -S /data/mysql/tmp/mysqld.sock
select user,host,authentication_string from mysql.user;

• %:主要允许从任何主机连接到MySQL服务器，即外部连接
• localhost: 代表只允许本地主机连接到MySQL服务器，即本地连接。（本地主机就是MySQL服务器所在的本地主机，就是运行MySQL服务的主机）
• 127.0.0.1：使用TCP/IP的方式进行网络通信，也属于本地连接。（与localhost的区别是，localhoast是可以使用套接字socket进行连接）

上下两张图，可以看出127.0.0.1和localhost区别，localhost可以使用套接字连接，127.0.0.1必须要配合-h -P连接，且可以不带套接字连接

二 修改root用户的host

Mysql8.0，使用root用户修改root的host，使用grant语法会一直报错，只能使用update语法修改

SELECT user, host FROM mysql.user WHERE user='root';
UPDATE mysql.user SET host='new_host' WHERE user='root' AND host='current_host';

TIPS：mysql8.0每个host对应的用户都算新用户，（理解不一定正确）需要重新创建该字段的用户再授权，使用下三中文档创建 

三 创建远程用户&远程用户白名单

https://www.cnblogs.com/dongxt/p/14883465.html

##lxy@'10.0.0.10'  lxy只能在10.0.0.10这个客户端登录
create user lxy@'10.0.0.10' identified by '123123';

四 修改密码

root用户修改普通用户密码：

mysql> ALTER USER  www@'127.0.0.1'   IDENTIFIED BY 'www666';
Query OK, 0 rows affected (0.00 sec)mysql> select user();
+----------------+
| user()         |
+----------------+
| root@localhost |
+----------------+
1 row in set (0.00 sec)

普通用户修改自己的密码：在有权限的情况下，直接使用alter修改，set password好像不可以

/usr/local/mysql/bin/mysql -p'www666' -uwww -h127.0.0.1  -P3307mysql> set password=password('aaa666');
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'password('aaa666')' at line 1mysql> ALTER USER 'www'@'127.0.0.1' IDENTIFIED BY 'aaa666';
Query OK, 0 rows affected (0.02 sec)

五 删除用户 

一个用户有两个网段权限，不可以直接drop username;

六 授权规则语法&授权/回收权限

grant      all privileges     on *.*      to lxy@'%'        with grant option;
授权          权限                库.表       用户@网段报名单

##创建一个ceshi用户，给予增删改查权限
mysql> create user ceshi@'%' identified by '123123';
Query OK, 0 rows affected (0.03 sec)mysql> grant SELECT,UPDATE,DELETE,INSERT on *.* to ceshi@'%' with grant option;
Query OK, 0 rows affected (0.01 sec)mysql> select user,host from mysql.user;
+------------------+-----------+
| user             | host      |
+------------------+-----------+
| bbb              | %         |
| beifen           | %         |
| ceshi            | %         |
| slave1           | %         |
| www              | 127.0.0.1 |
| lxy              | localhost |
| mysql.infoschema | localhost |
| mysql.session    | localhost |
| mysql.sys        | localhost |
| root             | localhost |
| www              | localhost |
+------------------+-----------+
11 rows in set (0.00 sec)#查询权限语句mysql> show grants for ceshi@'%';
+------------------------------------------------------------------------------+
| Grants for ceshi@%                                                           |
+------------------------------------------------------------------------------+
| GRANT SELECT, INSERT, UPDATE, DELETE ON *.* TO `ceshi`@`%` WITH GRANT OPTION |
+------------------------------------------------------------------------------+
1 row in set (0.00 sec)#回收delete权限mysql> REVOKE DELETE ON *.* from ceshi@'%'  ;
Query OK, 0 rows affected (0.09 sec)mysql> show grants for ceshi@'%';
+----------------------------------------------------------------------+
| Grants for ceshi@%                                                   |
+----------------------------------------------------------------------+
| GRANT SELECT, INSERT, UPDATE ON *.* TO `ceshi`@`%` WITH GRANT OPTION |
+----------------------------------------------------------------------+
1 row in set (0.00 sec)

七 root用户忘记怎么办

#配置文件加参数，跳过授权表
[mysqld]
skip-grant-tables

然后进去改密码，改完后，记得把配置文件改回来！