MySQL增加/删除用户、授权、修改密码
// 创建用户
mysql> use mysql;
mysql> insert into user(Host,User,Password) values('localhost','yongfu_a',password('my_password'));
// 刷新系统权限表
mysql> flush privileges;
//退出后登录一下
mysql>exit;
说明：
至此创建mysql的第二个用户：yongfu_a（第一个用户是root），他的密码是my_password。需要刷新系统权限表flush privilege，该用户才能生效登录。此时该用户（yongfu_a）仅有在本机（localhost）使用密码（my_password）登录的权 限，还没有其他权限，需要使用GRANT命令对该用户进行相应授权。
通过GRANT授权的方式新增用户
// 以root用户登录mysql
[yongfu]$ mysql -uroot -p
// 新增一个新用户yongfu_b
mysql> grant all privileges on *.* to yongfu_b@'192.168.1.%' identified by 'my_password_2';
说明：
至此创建了mysql的第三个用户：yongfu_b，他的密码是my_password_2。不需要使用flush privilege刷新系统权限表，改用户立即生效。此时该用户（yongfu_b）可以在192.168.1.0/24的网段上的任意机器使用密码 （my_password_2）登录。同时已经对所有库的所有表赋予了全部权限
ps:使用grant方法新增用户更方便也更省事。只需要一步就可以完成新增用户和用户授权的全部操作
2. MySQL修改用户密码
2.1 直接修改数据库修改密码
// 在数据库中修改密码字段
mysql> use mysql
mysql> update user set Password = password("new_password") where User = "yongfu_a" and Host="localhost";
mysql> flush privileges;
2.2 通过GRANT方法修改密码
// 其实就是新增用户那个方法，grant本身是授权、授予的意思。
// 修改用户yongfu_b的密码为 my_password_new
mysql> grant all privileges on *.* to yongfu_b@'192.168.1.%' identified by 'my_password_new';
3. 授权和取消权限
3.1 授权mysql使用GRANT命令对用户进行授权。前面我们已经数次接触到GRANT命令，用它添加了一个用户，也为用户修改了密码，同时为yongfu_a用户授予了SUPER权限。其实GRANT设计的目的本身只是为了授权的。
// 首先我们查看 yongfu_a 用户有哪些权限
mysql> select * from user where User='yongfu_a' /G;
*************************** 1. row ***************************
Host: localhost
User: yongfu_a
Password: *1603BD6A73604A872220561294D3C5916A7B1E60
Select_priv: N
Insert_priv: N
Update_priv: N
Delete_priv: N
Create_priv: N
省略后面的
**************************************************************************************************************
// 从上面可以看出，yongfu_a 用户只有前面授权的SUPER权限。
// 怎么给yongfu_a用户授予增删改查的权限？使用如下命令：
mysql> GRANT SELECT,UPDATE,INSERT,DELETE on *.* to yongfu_a@'localhost';// 再查看下权限情况：
mysql> select * from user where User='yongfu_a' /G;*************************** 1. row ***************************
Host: localhost
User: yongfu_a
Password: *1603BD6A73604A872220561294D3C5916A7B1E60
Select_priv: Y
Insert_priv: Y
Update_priv: Y
Delete_priv: Y
********************************************************
// 这时已经被授予了增删改查的权限了，同时发现SUPER权限还是保留的。
3.2 取消授权// REVOKE语句的语法格式如下：
// 其中privileges是要取消的权限，user是要被取消权限的用户名， 特别注意user前的关键字变为了from。
REVOKE privileges (columns) on what from user ;
// 取消 yongfu_a用户的增删改查权限
mysql> REVOKE SELECT,UPDATE,INSERT,DELETE on *.* from yongfu_a@'localhost';
mysql> select * from user where User='yongfu_a' /G;
就可以看到，被取消了增删改查的权限了
REVOKE语句用于取消用户的权限，而不可以删除用户。
4. 删除用户取消了所有的权限，用户仍然可以连接到服务器。要想彻底的删除用户，必须使用DELETE语句将该用户的记录从mysql数据库中的user表中删除。
// 使用DELETE删除用户yongfu_a，代码如下：
mysql> use mysql
Database changed
mysql> delete from user where user='yongfu_a' and host='localhost' ;
mysql>flush privileges ;
Query OK, 1 row affected (0.02 sec)
其中，delete用于删除用户，flush告诉服务器重新加载授权表。
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