pdo连接数据库

const USER ='root';      //数据库连接用户名

const PASS='root';          //对应的密码

const DSN ="mysql:host=localhost;dbname=databasename";

class Db{

    //保存实例的私有静态变量

    private static $conts;

    //构造函数和克隆函数都声明为私有的

    private function __construct(){

    }

    private function __clone(){

        //实现

    }

    //访问实例的公共静态方法

    public static function getInstance(){

        if(self::$conts ){

            return self::$conts;

        }else{

            try {

                $dbh = new PDO(DSN, USER, PASS); //初始化一个PDO对象

            } catch (PDOException $e) {

                die ("Error!: " . $e->getMessage() . "<br/>");

            }

            self::$conts = $dbh;

            return self::$conts;

        }

    }

}

    $db = Db::getInstance();

   //查看交易是否到期

    $sth=$db->query('SELECT * FROM qianzhui_countdown',PDO::FETCH_ASSOC);

    $re=$sth->fetchAll();

    foreach($re as $vo){

       if($vo['end_time']<time()){

            $sql = 'delete from qianzhui_countdown where id='.$vo['id'];

            $item = $db->exec($sql);

            //其他数据库操作

       }

   }