警告：mysqli_stmt_bind_result()：绑定变量的数量与准备语句中的字段数量不匹配

Question

我正在做一个登录表单，由于我昨天刚刚了解了准备好的语句，所以我被代码困住了。我不断收到此错误：

Warning: mysqli_stmt_bind_result(): Number of bind variables doesn't match number of fields in prepared statement.

我需要一些关于如何使用该功能的启发。我只包含了与我的问题相关的代码。

// Validate credentials
if(empty($email_err) && empty($password_err) && empty($userLevel_err)){
    // Prepare a select statement
    $sql = "SELECT id, email, password FROM users WHERE email = ? AND userLevel=?";
    
    if($stmt = mysqli_prepare($link, $sql)){
        // Bind variables to the prepared statement as parameters
        mysqli_stmt_bind_param($stmt, "ss", $param_email, $param_userLevel);
        
        // Set parameters
        $param_email = $email;
        $param_userLevel = $userLevel;
        
        // Attempt to execute the prepared statement
        if(mysqli_stmt_execute($stmt)){
            // Store result
            mysqli_stmt_store_result($stmt);
            
            // Check if email exists, if yes then verify password
            if(mysqli_stmt_num_rows($stmt) == 1){                    
                // Bind result variables
                mysqli_stmt_bind_result($stmt, $id, $email, $hashed_password, $userLevel);
                if(mysqli_stmt_fetch($stmt)){
                    if(password_verify($password, $hashed_password)){
                        // Password is correct, so start a new session
                        session_start();
                        
                        // Store data in session variables
                        $_SESSION["loggedin"] = true;
                        $_SESSION["id"] = $id;
                        $_SESSION["email"] = $email;                            
                        
                        // Redirect user to welcome page
                        header("location: index.php");
                        
                    } else{
                        // Display an error message if password is not valid
                        $password_err = "The password you entered was not valid.";
                    }
                

Answer 1

问题是绑定变量的数量与准备语句中的字段数量不匹配。您要么需要绑定更少的变量，要么需要将缺少的第四列添加到 SQL

//                                VVV Add the fourth column here
$sql = "SELECT id, email, password, userLevel FROM users WHERE email = ? AND userLevel=?";

或者绑定更少的变量

//                                                         VVV Remove the fourth binding
mysqli_stmt_bind_result($stmt, $id, $email, $hashed_password);