MySQL adiciona campos a um Enum

<?php

$sql = "select table_schema
             , table_name
             , column_name
             , column_type
             , is_nullable
             , column_default
          from information_schema
         where data_type = 'enum'";

$res = mysql_query($sql);

while ($row = mysql_fetch_assoc($res)) {

  // these are important -->       leading comma --v      close paren --v
  $new_enum = substr($row['column_type', 0, -1) . ",'new','enums','here')"

  $sql = "alter table `{$row['table_schema']}`.`{$row['table_name']}`";
  $sql .= " modify column `{$row['column_name']}`";
  $sql .= " $new_enum";
  $sql .= ($row['is_nullable'] == 'YES') ? " NULL" : " NOT NULL";
  $sql .= " default $row['column_default']";

  mysql_query($sql);
}