Sort table by column then add rank according to column

[my_filthy_mind]

I'd like to sort my table by a column descending, then update a "rank" field in the table according to the sort. So after sorting, the "rank" field in row 1 would be assigned the value of "1", the "rank" field in row 2 would be assigned the value of "2", etc. to the last row. Can anyone help with the code? Thanks.

[Pig]

yeah, just do a query that grabs the col name that you want to sort by, and the id. Then do a while statement that increments the rank, and do an update query.

$result = mysql_query("SELECT colname, id FROM table_name ORDER BY colname");

$i = 1;

while( $row = mysql_fetch_array($result) )
{
mysql_query("UPDATE table_name SET rank='$i'  WHERE id='$row[id]'");
$i++;
}