mysql5.7 Access denied for user 'root'@'localhost'

用

mysqld --skip-grant-tables

来重新启动mysql，然后再修改密码

UPDATE user SET authentication_string=PASSWORD('root') where USER='root'; 

可能会出现的问题：

ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.

解决：

SET PASSWORD = PASSWORD('123456');