How to remove this mysqli warning on bind result?

Question

I am getting a mysqli warning in my error report stating Warning: mysqli_stmt::bind_result() [mysqli-stmt.bind-result]: Number of bind variables doesn't match number of fields in prepared statement in ... on line 36 Does anyone know how I can bind the results correctly so that this warning can go away? I can't really see what the problem is but then saying this I am a beginner when it comes to using mysqli.

Below is the code:

<?php
  // PHP code
  session_start(); 

//connected to db

  // required variables (make them explciit no need for foreach loop)
  $teacherusername = (isset($_POST['teacherusername'])) ? $_POST['teacherusername'] : '';
  $teacherpassword = (isset($_POST['teacherpassword'])) ? $_POST['teacherpassword'] : '';
  $loggedIn = false;

  if (isset($_POST['submit'])) {

    $teacherpassword = md5(md5("j3Jf92".$teacherpassword."D203djS"));  

    // don't use $mysqli->prepare here
    $query = "SELECT * FROM Teacher WHERE TeacherUsername = ? AND TeacherPassword = ? LIMIT 1";
    // prepare query
    $stmt=$mysqli->prepare($query);
    // You only need to call bind_param once
    $stmt->bind_param("ss",$teacherusername,$teacherpassword);
    // execute query
    $stmt->execute(); 
    // get result and assign variables (prefix with db)
    $stmt->bind_result($dbTeacherForename,$dbTeacherSurname,$dbTeacherUsername,$dbTeacherPassword);

    while($stmt->fetch()) {
      if ($teacherusername == $dbTeacherUsername && $teacherpassword == $dbTeacherPassword) {
        $loggedIn = true;
      }
    }

    if ($loggedIn == true){
      // left your session code as is - but think wisely about using
      $_SESSION['teacherforename'] = $dbTeacherForename;
      $_SESSION['teachersurname'] = $dbTeacherSurname;
      header( 'Location: menu.php' ) ;
      die();
    }

       /* close statement */
    $stmt->close();

    /* close connection */
    $mysqli->close();
  }
?>

Answer 1

using the wildcard * is not recommend. probably there are more columns in the table than just the 4 you need?

I would go with

SELECT TeacherForname, TeacherSurname, TeacherUsername, TeacherPassword FROM Teacher WHERE TeacherUsername = ? AND TeacherPassword = ? LIMIT 1

Answer 2

The error is occurring because you're asking mysqli to bind x columns to y variables where x != y . How many columns are in the Teacher table?