php验证是否建立数据库，否，则自动建立

<?php
/*
默认建立的数据库为test,数据表为admin,管理员只需要修改DB_PWD（即本地的服务器密码）即可，用户密码采用md5加密
*/
define(DB_HOST,"localhost");
define(DB_USER,"root");
define(DB_PWD,"yuyouwen");
define(DB_NAME,"test");

$con=mysql_connect(DB_HOST,DB_USER,DB_PWD)or die("无法连接数据库服务器！");
mysql_select_db(DB_NAME,$con);
// Create database
if(!mysql_select_db(DB_NAME,$con)) {
    mysql_query("CREATE DATABASE test");
    if(mysql_select_db(DB_NAME,$con)){
    $query="CREATE table admin (
          `id` smallint(5) NOT NULL auto_increment,
          `username` varchar(35) NOT NULL,
          `password` varchar(35) NOT NULL,
          `email` varchar(35) NOT NULL,
          `regTime` varchar(35) NOT NULL,
          PRIMARY KEY  (`id`)
         )";
        mysql_query($query);        
    }
    }
?>