1、首次安装 root初始密码为空，注意就是没有密码，直接敲回车即可进入
注：在centos7下安装mysql5.6初次密码并不为空，而是生成了一个随机的密码。
A RANDOM PASSWORD HAS BEEN SET FOR THE MySQL root USER !
You will find that password in '/root/.mysql_secret'.
D:\wamp\bin\mysql\mysql5.6.17\bin>mysql -uroot -p
Enter password: [直接回车]
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 7
Server version: 5.6.17 MySQL Community Server (GPL)
Copyright (c) 2000, 2014,Oracleand/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>
2、修改root密码的几种方法：
1） 用SET PASSWORD命令
首先登录MySQL。
格式：mysql> set password for 用户名@localhost = password('新密码');
例如：
mysql>set password for root@localhost = password('root');
Query OK, 0 rows affected (0.00 sec)
mysql>quit
Bye
D:\wamp\bin\mysql\mysql5.6.17\bin>mysql -uroot -proot
Warning: Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 5.6.17 MySQL Community Server (GPL)
Copyright (c) 2000, 2014, 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>
2）用mysqladmin
格式：mysqladmin -u用户名 -p旧密码 password 新密码
例如：
D:\wamp\bin\mysql\mysql5.6.17\bin>mysqladmin -uroot -proot password root123
Warning: Using a password on the command line interface can be insecure.
D:\wamp\bin\mysql\mysql5.6.17\bin>mysql -uroot -proot123
Warning: Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 10
Server version: 5.6.17 MySQL Community Server (GPL)
Copyright (c) 2000, 2014, 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>
3）用UPDATE直接编辑user表
首先登录MySQL。
mysql> use mysql;
mysql> update user set password=password('root') where user='root' and host='localhost';
mysql> flush privileges;
--注意一定要flush privileges;
mysql 新设置用户或更改密码后需用flush privileges刷新MySQL的系统权限相关表，否则会出现拒绝访问，还有一种方法，就是重新启动mysql服务器，来使新设置生效。
4）在忘记root密码的时候，可以这样。
以windows为例：
1. 关闭正在运行的MySQL服务。
2. 打开DOS窗口，转到mysql\bin目录。
3. 输入mysqld --skip-grant-tables 回车。--skip-grant-tables 的意思是启动MySQL服务的时候跳过权限表认证。
4. 再开一个DOS窗口（因为刚才那个DOS窗口已经不能动了），转到mysql\bin目录。
5. 输入mysql回车，如果成功，将出现MySQL提示符 >。
6. 连接权限数据库： use mysql; 。
6. 改密码：update user set password=password('root123') where user='root';（别忘了最后加分号） 。
7. 刷新权限（必须步骤）：flush privileges;
8. 退出quit当前cmd，并且关闭2中的DOS窗口
9. 使用用户名root，新密码root123在4中DOS窗口登录。