$stmt = $db->prepare("SELECT * FROM users WHERE user=?");
    $stmt->bind_param("s", $username);
    $stmt->execute();
    $result = $stmt->get_result();
    if ($stmt->num_rows == 1) {
    $row = $result->fetch_assoc();
    $password = $row["pass"];
    // Check Password
    if ($pass == $password) {
    // Some Operations
  }
}