代码可能是这么写的：
//to make a connection with database $conn = mysql_connect("localhost", "root", "password") or die(mysql_error());在某些情况下，你改成下面就可以解决：
$conn = mysql_connect("localhost", "root") or $conn = mysql_connect("localhost", "root", "")
但是，有些情况下它的根本原因是你的当前数据库的用户没有获得多数据库访问的授权。
其实，最多的原因可能是你的数据库没有起来。O(∩_∩)O哈哈~
解决方法是你启动数据库。
这种情况下的表现是：
1.在命令行下：
forlong401:Documents forlong401$ sudo mysql --user=root -p
Enter password:
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)
2. 在浏览器上：
Deprecated: mysql_connect(): The mysql extension is deprecated and will be removed in the future: use mysqli or PDO instead in /Library/WebServer/Documents/qa/qa-include/qa-db.phpon line 68
Warning: mysql_connect(): Access denied for user 'root'@'localhost' (using password: YES) in /Library/WebServer/Documents/qa/qa-include/qa-db.php on line 68
Could not establish database connection. Please check the username, password and hostname in the config file, and if necessary set up the appropriate MySQL user and privileges.
3. 在phpmyadmin上：
#2002 无法登录 MySQL 服务器