php - 尝试修复从 MYSQL 收到的错误时遇到问题

Question

这是我的 PHP 代码，它导致了这个错误，我以前没有遇到过这个错误，我在发布之前进行了搜索和查看，但找不到解决该错误的方法。

PHP(正在运行的 PHP):

   <?php 
    require('includes/config.php'); 
    $username = $_SESSION['username'];

    if($_POST['username'] != $_SESSION['user']['username']) 
    { 
        // Define our query parameter values 
        $query_params = array( 
            ':username' => $_POST['username']
        );

        $stmt = $db->prepare("SELECT username FROM members WHERE username = :username"); 
        $stmt->execute($query_params);

        // Retrieve results (if any) 
        if($stmt->rowCount() > 0) 
        { 
            die("This username is already in use"); 
        }

        try 
        { 
            $query_params = array( 
                ':username' => $_POST['username'],
                ':last_username' => $username
            );

            // Execute the query 
            $stmt = $db->prepare("UPDATE members SET username = :username WHERE username = :last_username"); 
            $result = $stmt->execute($query_params); 
        } 
        catch(PDOException $ex) 
        { 
            // Note: On a production website, you should not output $ex->getMessage(). 
            // It may provide an attacker with helpful information about your code.  
            die("Failed to run query: " . $ex->getMessage()); 
        } 
          } 

?>

HTML:

                               <div id="changeusername" class="tab-pane">
                     <h3> Change Your Username : </h3>                  
  <form  method="post" action="changeusername.php" autocomplete="off">
                    <input type="text" name="username" id="username" class="form-control" placeholder="New Username" autofocus  value="<?php if(isset($error)){ echo $_POST['username']; } ?>" tabindex="1">
                    <br>
                    <input type="password" name="password" id="password" class="form-control" placeholder="Confirm Your Password">
                   <br>
                    <button class="btn btn-theme btn-block" name="submit" type="submit"><i class="fa fa-lock"></i> Change Username</button>


              </form>       

当我输入 Boom2(新用户名)和oom1(旧用户名)后，我接收错误:无法运行查询:SQLSTATE[42000]:语法错误或访问冲突:1064 您的 SQL 语法有错误；检查与您的 MySQL 服务器版本相对应的手册，了解在第 1 行 ''boom2' WHERE username = 'boom1'' 附近使用的正确语法

Answer 1

如果用户名存在，我会重写您的 php 代码以出错，并更正您的更新查询。请尝试一下:

<?php 
    require('includes/config.php'); 
    $username = $_SESSION['username'];

    if($_POST['username'] != $_SESSION['user']['username']) 
    { 
        // Define our query parameter values 
        $query_params = array( 
            ':username' => $_POST['username']
        );

        $stmt = $db->prepare("SELECT username FROM members WHERE username = :username"); 
        $stmt->execute($query_params);

        // Retrieve results (if any) 
        if($stmt->rowCount() > 0) 
        { 
            die("This username is already in use"); 
        }

        try 
        { 
            $query_params = array( 
                ':username' => $_POST['username'],
                ':last_username' => $username
            );

            // Execute the query 
            $stmt = $db->prepare("UPDATE members SET username = :username WHERE username = :last_username"); 
            $result = $stmt->execute($query_params); 
        } 
        catch(PDOException $ex) 
        { 
            // Note: On a production website, you should not output $ex->getMessage(). 
            // It may provide an attacker with helpful information about your code.  
            die("Failed to run query: " . $ex->getMessage()); 
        } 

    } 

?>