问如何检查用户名和密码是否与数据库值匹配

EN

  $usersPassword = $_POST['password']);
  $hash = password_hash( $usersPassword , PASSWORD_DEFAULT );
  // you then store the username and the hash in your dbms. 
  // the column holding the hash should be VARCHAR(255) for future-proofing
  // NEVER! store the plain text (unhashed) password in your database

 $usersPassword = $_POST['password']);
 $valid = password_verify ( $usersPassword, $hash );
 if ( $valid ) {
   if ( password_needs_rehash ( $hash, PASSWORD_DEFAULT ) ) {
     $newHash = password_hash( $usersPassword, PASSWORD_DEFAULT );
     /* UPDATE the user's row in `log_user` to store $newHash */
   }
   /* log the user in, have fun! */
 }
 else {
  /* tell the would-be user the username/password combo is invalid */
 }

mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT); // enable exceptions

$conn = new mysqli($servername, $mysql_username, $mysql_password, $databaseName);

$log_username = $_POST['username'];
$log_password = $_POST['password'];

$sql = "SELECT log_username, log_password_hash FROM login WHERE log_username=?";
$stmt = $conn->prepare($sql);
$stmt->bind_param('s', $log_username);
$stmt->execute();
$result = $stmt->get_result();

while ($row = $result->fetch_assoc()) {
    if (password_verify($log_password, $row['log_password_hash'])) {
        $message = "ok";
        // header must be called before any other output
        header("Location: Doctors.php");
        exit();
    }
}
$message = "No";
// header must be called before any other output
header("Location: Doctors.php");

$un = $_POST['username'];
$pw = $_POST['password'];
print $pass . "_" . $email;

$query = mysqli_query($conn, "SELECT log_username,log_password FROM login WHERE log_username='$un' AND log_password='$pw'");

$result_can = mysqli_query($conn, $query);

while ($row = mysql_fetch_assoc($result_can)) {
    $check_username = $row['username'];
    $check_password = $row['password'];
}
if ($un == $check_username && $pw == $check_password) {
    $message = "ok";
    echo "<script type='text/javascript'>alert('$message');</script>";
    header("Location: Doctors.php");
} else {
    $message = "No";
    echo "<script type='text/javascript'>alert('$message');</script>";
    header("Location: Doctors.php");
}

if (mysqli_num_rows($query) > 0) {
    $message = "ok";
    echo "<script type='text/javascript'>alert('$message');</script>";
    header("Location: Doctors.php");
} else {
    $message = "No";
    echo "<script type='text/javascript'>alert('$message');</script>";
    header("Location: Doctors.php");
}

if (mysqli_num_rows($query) > 0) {
    echo "<script type='text/javascript'>alert('ok'); window.location.href='Doctors.php';</script>";
} else {
    echo "<script type='text/javascript'>alert('No'); window.location.href='Doctors.php';</script>";
}