php - 尝试切换到 PDO，随机图像脚本并不总是触发

Question

我正在尝试切换到 PDO。尽管我很快遇到了一些问题，但我无法解决的一个问题是我的随机图像脚本。我之前有一篇文章提到此功能不起作用，它与 SELECT MAX(id) 需要为 SELECT MAX(id-6) 有关。之前的问题是我得到的是随机数量的随机图像，而不是 6。

现在的问题是，有时我得到六张随机图像，有时我什么也得不到。我希望有人可以查看我的脚本，看看他们是否能发现其中的任何问题。

谢谢，有时只需第二双眼睛即可:

<?php
$passed_cat = mysql_real_escape_string($_GET['cat']);
$passed_sub_cat = mysql_real_escape_string($_GET['sub_cat']);

include ('../../connection.php');

$related_images = "SELECT *,r1.id as main_id 
                   FROM images AS r1 
                   JOIN 
                   (
                        SELECT ROUND(RAND() * (SELECT MAX(id-6) 
                                               FROM images)) AS id
                    ) AS r2 
                    WHERE r1.id >= r2.id 
                        AND public_approved='Approved'
                        AND category = :category
                        AND sub_category = :sub_category
                    ORDER BY r1.id ASC 
                        LIMIT 6
                            OFFSET 20";

$q = $conn->prepare($related_images);
$q->execute(array(
':category' => $passed_cat,
':sub_category' => $passed_sub_cat));


if(!$q)
{
    die("Query failed due to: ". $conn->errorInfo());
}

$q->setFetchMode(PDO::FETCH_BOTH);

while($row = $q->fetch())
{
echo "<div style='float:left; margin:2px;' >";
echo '<a href="sub_page.php?cat='. $passed_cat .'&sub_cat='. $passed_sub_cat .'&id='. $row['main_id'] .'"><img src="../../files/small/thumb0_'. $row['item_name'] . '.' . $row['file_extension'] . '" style="width:96px;" border="0"></a>';
echo "</div>";
}
?>

编辑:Connection.php

<?php

    $host = "localhost"; 
    $dbname = "all_sites";
    $db_username = "root";
    $db_password = "password";

try {
    $conn = new PDO("mysql:host=$host;dbname=$dbname",$db_username,$db_password);
}
catch (PDOException $pe)
{
    die('Connection error, due to: ' .$pe->GetMessage());
}
?>

Answer 1

mysql_real_escape_string() 不是必需的，如果不使用 mysql_connect() 可能会导致问题

From the manual: mysql_real_escape_string('',*link_identifier)

• The MySQL connection. If the link identifier is not specified, the last link opened by mysql_connect() is assumed. If no such link is found, it will try to create one as if mysql_connect() was called with no arguments. If no connection is found or established, an E_WARNING level error is generated.

只需将 $_GET 变量传递给执行数组即可:

$q->execute(array(':category'=>$_GET['cat'], ':sub_category'=>$_GET['sub_cat']));