PHP kôd:
$q = mysql_query("SELECT id FROM tabela GROUP BY polje HAVING count(*)>1");
while($row = mysql_fetch_row($q))
$ids[] = $row[0];
mysql_query(sprintf("DELETE FROM tabela WHERE id IN (%s)", implode(',', $ids)));
tako nekako... naravno, treba proveriti i greske i tako to...