1.设置数据库密码
#1.简单的设置方式
[root@db01 ~]# mysqladmin -uroot password '123'
Warning: Using a password on the command line interface can be insecure.
#2.安全的设置方式
[root@db02 ~]# mysqladmin -uroot password
New password: 123
Confirm new password: 123
2.使用密码登录数据库
#1.正确的登陆方式（不标准，不安全）
[root@db01 ~]# mysql -uroot -p123
[root@db01 ~]# mysql -u root -p123
#2.正确的登陆方式（标准，安全）
[root@db01 ~]# mysql -u root -p
Enter password:
#3.错误的登陆方式（会把密码当成数据库）
[root@db01 ~]# mysql -u root -p 123
Enter password:
ERROR 1049 (42000): Unknown database '123'
for password options, the password value is optional: If you use a -p or --password option and specify the password value, there must be no space between -p or --password= and the password following it.
#如果使用-p或者--password参数，他们与密码之间不能有空格
If you use a -p or --password option but do not specify the password value, the client program prompts you to enter the password. The password is not displayed as you enter it. This is more secure than giving the password on the command line. Other users on your system may be able to see a password specified on the command line by executing a command such as ps auxw.
#如果只写-p或--password参数什么都不接，意思是让你手动输入密码
#4.登录数据库后直接进入库中
[root@db01 ~]# mysql -u root -p mysql
Enter password:
3.查询数据库用户
mysql> select user,host from mysql.user;
+------+-----------+
| user | host |
+------+-----------+
| root | 127.0.0.1 |
| root | ::1 |
| | db01 |
| root | db01 |
| | localhost |
| root | localhost |
+------+-----------+
6 rows in set (0.00 sec)
4.删除没有用的用户（优化）
mysql> drop user root@'::1';
Query OK, 0 rows affected (0.00 sec)
mysql> drop user ''@'localhost';
Query OK, 0 rows affected (0.00 sec)
mysql> drop user ''@'db01';
Query OK, 0 rows affected (0.00 sec)
mysql> delete from mysql.user where host='db01';
Query OK, 1 row affected (0.00 sec)
mysql> select user,host from mysql.user;
+------+-----------+
| user | host |
+------+-----------+
| root | 127.0.0.1 |
| root | localhost |
+------+-----------+
2 rows in set (0.00 sec)