mysql> create database yan1; 
ERROR 1820 (HY000): You must SET PASSWORD before executing this statement 
mysql> SET PASSWORD = PASSWORD('123456'); 
Query OK, 0 rows affected (0.03 sec) 
mysql> create database yan1; 
Query OK, 1 row affected (0.00 sec) 

# mysql -u root -p 
Enter password: 
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO) 

# mysql -u root -p password 'newpassword' 
Enter password: 
mysqladmin: connect to server at 'localhost' failed 
error: 'Access denied for user 'root'@'localhost' (using password: YES)' 

# /etc/init.d/mysql stop 
# mysqld_safe --user=mysql --skip-grant-tables --skip-networking & 
# mysql -u root mysql 
mysql> UPDATE user SET Password=PASSWORD('newpassword') where USER='root' and host='root' or host='localhost';//把空的用户密码都修改成非空的密码就行了。 
mysql> FLUSH PRIVILEGES; 
mysql> quit # /etc/init.d/mysqld restart 
# mysql -uroot -p 

mysql> SET PASSWORD = PASSWORD('123456'); 
Query OK, 0 rows affected (0.03 sec) 
mysql> create database roger; 
Query OK, 1 row affected (0.00 sec)