1、停止 服务 

PS C:\WINDOWS\system32> net stop mysql
mysql 服务正在停止.
mysql 服务已成功停止。

2、执行 mysqld --shared-memory --skip-grant-tables

PS C:\WINDOWS\system32> mysqld --shared-memory --skip-grant-tables

------以下操作 另外打开一个 终端-----

3、 执行 mysql

PS C:\WINDOWS\system32> mysqlWelcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 7
Server version: 8.0.17 MySQL Community Server - GPLCopyright (c) 2000, 2019, 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.

4、执行指令 FLUSH PRIVILEGES; 刷新权限

mysql> FLUSH PRIVILEGES;Query OK, 0 rows affected (0.05 sec)

5、修改root密码为123456

mysql> ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY '123456';Query OK, 0 rows affected (0.02 sec)

6、退出mysql

mysql> quitBye

7、在第一个窗口 退出执行的任务  

8、重新启动 mysql

PS C:\WINDOWS\system32> net start mysqlmysql 服务正在启动 ..
mysql 服务已经启动成功。

9、重新登录mysql

PS C:\WINDOWS\system32> mysql -u root -pEnter password: ******Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 8.0.17 MySQL Community Server - GPLCopyright (c) 2000, 2019, 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>