sortable with php question

sortable with php question

most sortable sample online tech you get the list id and update the position, for example

  1. foreach ($_GET['listItem'] as $position => $item) {
  2.   $sql = "UPDATE table SET position = $position WHERE id = $item"; 
  3. }

but actually, we usually use another filed to save the position, maybe like
id  label position
2    A       7
6    B      11
9    C      14

if I exchange the first and second data and save, it should be like
id  label position
6    B       7
2    A      11
9    C      14

but if we use the sample to do that, it always make the position like
id  label position
6    B       0
2    A       1
9    C       2

it's totally wrong, how to make it right?