昨天安装mysql-5.5.20-winx64.msi 安装成功 ，今天卸载了 。再安装就给提示，网上说给文件夹删了。不好用

The security settings could not be applied to the database because the connection has failed with the following error.

Error Nr. 1045
Access denied for user 'root'@'localhost' (using password: NO)

If a personal firewall is running on your machine, please make sure you have opened the TCP port 3306 for connections. Otherwise no client application can connect to the server. After you have opened the port please press [Retry] to apply the security settings.

If you are re-installing after you just uninstalled the MySQL server please note that the data directory was not removed automatically. Therefore the old password from your last installation is still needed to connect to the server. In this case please select skip now and re-run the Configuration Wizard from the start menu.

原因是mysql没有卸载干净。

1 你把 我的电脑 里面的隐藏文件也显示出来，C:\Documents and Settings\All Users\Application Data下面有个mysql文件夹删除。
2 进入 注册表，找到HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\Eventlog\Application\MySQL删除
3 进入 注册表，找到HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Services\Eventlog\Application\MySQL删除，然后重新安装，就行了。

很明显你之前是装过了,而且还没删除就来重装.真是.......no zuo no die 第一个选项是让你修改已安装的mysql , 第二个选项是修复 你已安装的mysql 第三个是删除你的mysql

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