回答

只要设置$db->setAttribute (\PDO::ATTR_PERSISTENT, true);就好了，代码如下：

<?php

$outhtml = "";

try {

    $db = new PDO('mysql:host=localhost;dbname=guest', 'guest', 'p6yhG8iDRMNxdJ9w');



    $db->setAttribute (\PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION);

    $db->setAttribute (\PDO::ATTR_PERSISTENT, true);

    $res = $db->prepare("select * from User"); //准备查询语句

    $res->execute();

    while ($row = $res->fetch(PDO::FETCH_ASSOC)) {

        if (empty($key)) {

            $key = array_keys($row);



            $outhtml .= "<tr>";

            foreach ($key as $item) {

                $outhtml .= "<th>{$item}</th>";

            }

            $outhtml .= "</tr>";

        }

        $values = array_values($row);

        $outhtml .= "<tr>";

        foreach ($values as $item) {

            $outhtml .= "<td>{$item}</td>";

        }

        $outhtml .= "</tr>";

    }





} catch (\PDOException $e) {



    $outhtml .= $e->getMessage();



}

echo $outhtml."\n";

$db = null; //关闭数据库