MySQL错误：ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

From terminal I enter（终端输入）:

mysql -u root

which outputs this error（输出错误为）:

ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

To try and resolve it I stopped mysql from ‘System Preferences’, then from terminal typed:（为了解决这个问题，从‘System Perferences’结束mysql）

sudo mysqld_safe —skip-grant-tables

I opened a second tab and entered(再一次启动mysql):

mysql -u root

Then from in mysql（显示）:

update mysql.user set password_expired = 'N', authentication_string=PASSWORD('newpassword') where user = 'root';

解决办法：
For security reason mysql -u root want work untill you pass -p in command so try with below way.(由于安全原因，mysql -u root在遇到pass -p的时候才能开始工作)

 mysql -u root -p[Enter] //enter your localhost password

所以，在终端输入上述命令，mysql -u root -p，回车输入密码即可。