PHP的MySQL - 檢查主題名稱是否已經存在

Question

我的代碼不能正常工作，檢查是否主題名稱是已經存在使用PHP SQL注入預處理語句：

代碼：

<?php 
if($_GET["action"] == "post") { 
$servername = "localhost"; 
$username = "MY DB"; 
$password = "MY PASS"; 
$dbname = "MY DB"; 
// Create connection 
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT); 
$conn = new mysqli($servername, $username, $password, $dbname); 
// Check connection 
if ($conn->connect_error) { 
    die("Connection failed: " . $conn->connect_error); 
} 

$checkSubject = $conn->prepare("SELECT * FROM IndexData WHERE SubjectName = ?"); 
$checkSubject->bind_param('s', $_POST['filename']); 
$checkSubject->execute(); 
$checkSubject->store_result(); 
$countSubject = $checkSubject->num_rows; 
//Create or Edit Files 
    if(strlen($_POST['filename']) <= 30 && strlen($_POST['filename']) >= 8 && strlen($_POST['comment']) >= 100 && strlen($_POST['comment']) <= 5000 && strlen($_POST['description']) >= 50 && strlen($_POST['description']) <= 500 && strlen($_POST['userSName']) >= 10 && strlen($_POST['userSName']) <= 20) { 
if ($countSubject > 0) { 
    $echoTxt = " <pre>Subject Has Been Posted! 
    Link: <a href=\"Code-Blog-Index-Posts.php?SubjectName=" . $_POST['filename'] . "\" target=\"_blank\">Click Me</a></pre> <br>"; 
    require("CreateDataPosts.php"); 
} else { 
    $echoTxt = die("<pre>[ERROR]Subject Already Exist!</pre>"); 
} 
    } else { 
    echo "<pre><span class=\"error\">Subject must Greater than 8 and Less than 30 characters</span></pre>"; 
    echo "<pre><span class=\"error\">Post must Greater than 100 and Less than 5000 characters</span></pre>"; 
    echo "<pre><span class=\"error\">Description must Greater than 50 and Less than 500 characters</span></pre>"; 
    die(); 
} 



echo $echoTxt; 
echo "<a name=\"PostResult\"></a>"; 
$countSubject->close(); 
$conn->close(); 
} 
?> 

，它總是返回到0
我不知道爲什麼，但 我希望你可以解決它的傢伙！，謝謝！

Answer 1

首先你要檢查是否有一個同名的字段。因此，您的查詢需要返回0或1.

# IF VALUE = 0/FIELD NOT FOUND - NO EXISTS 

if($countSubject == 0) 
{ 

    # the query needs to return 0 to post the new subject, if the returned value is over 0, so exists 

    $echoTxt = "<pre>Subject Has Been Posted! Link: <a href=\"Code-Blog-Index-Posts.php?SubjectName=" . $_POST['filename'] . "\" target=\"_blank\">Click Me</a></pre> <br>"; 

    require("CreateDataPosts.php"); 

} 
else $echoTxt = die("<pre>[ERROR]Subject Already Exist!</pre>");