mysql5.7后，默认会初始化一个随机密码在日志文件中。
1.默认随机密码会过期，提示如下
mysql> show databases;
ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.
解决办法：
2.SET PASSWORD = PASSWORD(‘your new password‘);
3. ALTER USER ‘root’@’localhost’ PASSWORD EXPIRE NEVER;
4.flush privileges;