php 封装了一个PDO 类，看看有什么改进，和错误

class PdoHelper {

    private $dsn;
    private $usn;
    private $pwd;
    private $options;

    function __construct($dsn, $usn, $pwd, $options = array(PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8')) {
        $this->dsn = $dsn;
        $this->usn = $usn;
        $this->pwd = $pwd;
        $this->options = $options;
    }

    public function GetPDOStatement() {
        return new PDO($this->dsn, $this->usn, $this->pwd, $this->options);
    }

    //获得数据集
    public function GetData($sql, $parames = array()) {
        $dbh = $this->GetPDOStatement();

        if (count($parames) > 0) {
            $stmt = $dbh->prepare($sql);

            $keys = array_keys($parames);

            foreach ($keys as $key) {
                $stmt->bindValue($key, $parames[$key]);
            }

            $stmt->execute();

            return $stmt->fetchAll();
        } else {
            $query = $dbh->query($sql);
            if ($query) {
                return $query->fetchAll();
            }
        }

        return FALSE;
    }

    //获得数据行
    public function GetRow($sql, $parames = array()) {
        $dbh = $this->GetPDOStatement();
        if (count($parames) > 0) {
            $stmt = $dbh->prepare($sql);

            $keys = array_keys($parames);
            foreach ($keys as $key) {
                $stmt->bindValue($key, $parames[$key]);
            }

            $stmt->execute();
            return $stmt->fetch();
        } else {
            $query = $dbh->query($sql);

            if ($query) {
                return $query->fetch();
            }
        }

        return FALSE;
    }

    //获得一个值
    public function GetValue($sql, $parames = array()) {
        $dbh = $this->GetPDOStatement();

        if (count($parames) > 0) {
            $stmt = $dbh->prepare($sql);
            $keys = array_keys($parames);
            foreach ($keys as $key) {
                $stmt->bindValue($key, $parames[$key]);
            }

            $stmt->execute();

            return $stmt->fetchColumn();
        } else {
            $query = $dbh->query($sql);

            if ($query) {
                return $query->fetchColumn();
            }
        }

        return FALSE;
    }

    //执行一条查询
    public function Execute($sql, $parames = array()) {
        $dbh = $this->GetPDOStatement();

        if (count($parames) > 0) {
            $stmt = $dbh->prepare($sql);
            $keys = array_keys($parames);
            foreach ($keys as $key) {
                $stmt->bindValue($key, $parames[$key]);
            }

            return $stmt->execute();
        } else {
            return $dbh->exec($sql);
        }
    }

    //执行插入 并且返回最后插入的ID
    public function InsertDataGetLastID($sql, $parames = array()) {
        $dbh = $this->GetPDOStatement();
        if (count($parames) > 0) {
            $stmt = $dbh->prepare($sql);
            $keys = array_keys($parames);
            foreach ($keys as $key) {
                $stmt->bindValue($key, $parames[$key]);
            }
            $stmt->execute();
            return $dbh->lastInsertId();
        } else {

            $dbh->exec($sql);
            return $dbh->lastInsertId();
        }
    }

}
//该片段来自于http://outofmemory.cn