Question

I have a file hosting site where I provide a point for every unique download to user.

Sample of my table

These points can be redeemed by user. So for example if a user redeems 100 points than what is the best query to reduce points available from each row till 100 points are reduced.

Thank You.

Answer 1

Alright, then, here’s the SQL-dumb way I would do it. Hopefully an SQL guru will come around with a better solution. Note: This is pure pseudocode; write your own code based on this–it’s not going to work out of the box.

$total_to_deduct = 100;

// Each time, get the row with the highest points
$top_points_query = "SELECT id, points FROM my_table ORDER BY points DESC LIMIT 1;"

do {
  $result = do_query($top_points_query);

  if($result) {
    // I'm assuming you don't want to deduct more points from a row than it has
    $num_to_deduct = min($result['points'], $total_to_deduct);

    // Now deduct the points from the row we got earlier
    $update_query = "UPDATE my_table SET points = points - $num_to_deduct
                     WHERE id = $result['id']";

    if(do_query($update_query)) {
      $total_to_deduct -= $num_to_deduct;
    }
  }
} while($total_to_deduct > 0); // If we still have points to deduct, do it again