问如何在同一个mysql记录中插入和更新一个数字？

EN

$selectQuery = "SELECT points FROM table_loyalty WHERE username=" . $username . ";"

$selectResult = mysql_db_query($db, $selectQuery, $connection);

// if no results could be found
if (mysql_num_rows($selectResult) == 0) {
  //Presuming this is the order price?
  $newpoints = $row["price"] * 1000;

  $insertQuery = "INSERT into table_loyalty (username, orderno, points) VALUES ('$username', '$this_orderno', '$newpoints')";
  $insertResult = mysql_db_query($db, $insertQuery, $connection);
  // I personally have no idea what the check_mysql() function does, I presume its a function of you own making? With that I'm making the assumption that it handles the result in some way? 
  check_mysql($insertResult);

//results have been found
} else {
  $existingPoints = 0;
  while ($row = mysql_fetch_assoc($result)) {
    //There is a catch here. If used in this way you need to make sure that every username only has 1 entry in the table_loyalty. So updating only 1 row per user also means you can ONLY have 1 record per user.
    $existingPoints = $row["points"];
  }

  $newPoints = $row["price"] * 1000;
  $totalPoints = $existingPoints + $newPoints;
  $updateQuery = "update table_loyalty set points='$totalPoints' WHERE username='$username'";

  $update = mysql_db_query($db,updateQuery , $connection);
  check_mysql($update);
}