mysql删除无用用户的方法实现

(1) 查看当前已存在账户
mysql> select user,host,password  from  mysql.user; 或下面的命令
#mysql> sELECT DISTINCT CONCAT('User: ''',user,'''@''',host,''';') AS query FROM mysql.user; 
+---------------------------------------+
| query                                 |
+---------------------------------------+
| User: 'root'@'127.0.0.1';             |   #不要删
| User: 'wenqiang'@'172.16.1.%';        |
| User: 'root'@'localhost';             |   #不要删
| User: 'root'@'localhost.localdomain'; |
+---------------------------------------+
4 rows in set (0.00 sec)

mysql> drop user wenqiang@'172.16.1.%';     #删除不需要的用户



(2) 授权用户时尽量不要使用%(该符号表示用户可以从任何地方都可以登陆)
授权格式：grant 权限 on 数据库.* to 用户名@用户所在网段 identified by "密码";
#只允许root用户从10.0.0.10登陆mysql并授予全库访问权限，同时为root用户设置密码123456
mysql> grant all on *.* to root@'10.0.0.10' identified by '123456'; 

#这种情况是只授权，root用户可以使用空密码从本地登录
mysql> grant all on *.* to root@'localhost';

#这种情况是root用户可以从本地登录，同时设置密码abc123（root用户可以设置多套登录密码）
mysql> grant all on *.* to root@'localhost' identified by 'abc123';

(1)这样登陆上去，并增加一条localhost的权限
[root@localhost ~]# mysql -uroot -p -h 127.0.0.1  #通过127.0.0.1登录上去
mysql> grant all on *.* to root@'localhost' identified by 'abc123';  #在增加一条localhost的授权
mysql> flush privileges;

新增加的root用户可能没有最高权限，见第3.1

(1)登录mysql
[root@localhost ~]# mysql -uroot -p -h localhost
mysql> grant all on *.* to root@'localhost' identified by '123456';        
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES) #报错

(2)查看当前有哪些用户
mysql> SELECT DISTINCT CONCAT('User: ''',user,'''@''',host,''';') AS query FROM mysql.user;
+---------------------------------------+
| query                                 |
+---------------------------------------+
| User: 'root'@'127.0.0.1';             |  #使用 mysql -uroot -p -h127.0.0.1登录mysql授权没问题
| User: 'wenqiang'@'172.16.1.%';        |
| User: 'root'@'localhost';             |  #我发现从localhost登录的root用户无法给普通用户授权
| User: 'root'@'localhost.localdomain'; |
+---------------------------------------+
4 rows in set (0.00 sec)

(3)查看该root用户的Grant_priv选项是Y还是N(N表示无权给普通用户授权)
mysql> select * from mysql.user where User='root' and Host='localhost'\G;
*************************** 1. row ***************************
                  Host: localhost
                  User: root
              Password: *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9
           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: N     #无授权权限
       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: 
      password_expired: N
1 row in set (0.00 sec)

ERROR: 
No query specified

(3)把Grant_priv选项的N改为Y就可以了
mysql> update mysql.user set Grant_priv='Y' where User='root' and Host='localhost';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

(4)退出重新登录mysql，再次给普通用户授权(一定要先退出mysql)
mysql> grant all on *.* to root@'localhost' identified by '123456';    
Query OK, 0 rows affected (0.00 sec)